test: add test for this fix

Test~/MeshInfo2/MeshInfo2Test.cs

@@ -41,11 +41,17 @@ public class MeshInfo2Test
         [TestCase("two-negative-frame", 100, 10)]
 
         [TestCase("two-0-50-frame", -25, -2)]
-        [TestCase("two-0-50-frame", 0, -1)]
+        [TestCase("two-0-50-frame", 0, 0)]
         [TestCase("two-0-50-frame", 25, 0)]
         [TestCase("two-0-50-frame", 50, 1)]
         [TestCase("two-0-50-frame", 75, 2)]
 
+        [TestCase("single-0", -100, float.PositiveInfinity)]
+        [TestCase("single-0", -1, float.PositiveInfinity)]
+        [TestCase("single-0", 0, 0)]
+        [TestCase("single-0", 1, float.NegativeInfinity)]
+        [TestCase("single-0", 100, float.NegativeInfinity)]        
+
         public void BlendShapeLerp(string name, float weight, float offset)
         {
             var mesh = TestUtils.GetAssetAt<Mesh>($"MeshInfo2/{name}.asset");
@@ -63,6 +69,7 @@ public void BlendShapeLerp(string name, float weight, float offset)
 
         [TestCase("single-negative")]
         [TestCase("single-positive")]
+        [TestCase("single-0")]
         [TestCase("two-positive-frame")]
         [TestCase("two-negative-frame")]
         [TestCase("two-0-50-frame")]

Test~/MeshInfo2/single-0.asset

@@ -0,0 +1,190 @@
+%YAML 1.1
+%TAG !u! tag:unity3d.com,2011:
+--- !u!43 &4300000
+Mesh:
+  m_ObjectHideFlags: 0
+  m_CorrespondingSourceObject: {fileID: 0}
+  m_PrefabInstance: {fileID: 0}
+  m_PrefabAsset: {fileID: 0}
+  m_Name: single-0
+  serializedVersion: 10
+  m_SubMeshes:
+  - serializedVersion: 2
+    firstByte: 0
+    indexCount: 36
+    topology: 0
+    baseVertex: 0
+    firstVertex: 0
+    vertexCount: 8
+    localAABB:
+      m_Center: {x: 0, y: 0, z: 0}
+      m_Extent: {x: 1, y: 1, z: 1}
+  m_Shapes:
+    vertices:
+    - vertex: {x: -1, y: 0, z: 0}
+      normal: {x: 0, y: 0, z: 0}
+      tangent: {x: 0, y: 0, z: 0}
+      index: 4
+    - vertex: {x: -1, y: 0, z: 0}
+      normal: {x: 0, y: 0, z: 0}
+      tangent: {x: 0, y: 0, z: 0}
+      index: 5
+    - vertex: {x: -1, y: 0, z: 0}
+      normal: {x: 0, y: 0, z: 0}
+      tangent: {x: 0, y: 0, z: 0}
+      index: 6
+    - vertex: {x: -1, y: 0, z: 0}
+      normal: {x: 0, y: 0, z: 0}
+      tangent: {x: 0, y: 0, z: 0}
+      index: 7
+    shapes:
+    - firstVertex: 0
+      vertexCount: 4
+      hasNormals: 0
+      hasTangents: 0
+    channels:
+    - name: test0
+      nameHash: 4256558196
+      frameIndex: 0
+      frameCount: 1
+    fullWeights:
+    - 0
+  m_BindPose: []
+  m_BoneNameHashes: 
+  m_RootBoneNameHash: 0
+  m_BonesAABB: []
+  m_VariableBoneCountWeights:
+    m_Data: 
+  m_MeshCompression: 0
+  m_IsReadable: 1
+  m_KeepVertices: 1
+  m_KeepIndices: 1
+  m_IndexFormat: 0
+  m_IndexBuffer: 000001000200010003000200040005000000050001000000030001000700010005000700020003000600030007000600000002000400020006000400050004000700040006000700
+  m_VertexData:
+    serializedVersion: 3
+    m_VertexCount: 8
+    m_Channels:
+    - stream: 0
+      offset: 0
+      format: 0
+      dimension: 3
+    - stream: 0
+      offset: 0
+      format: 0
+      dimension: 0
+    - stream: 0
+      offset: 0
+      format: 0
+      dimension: 0
+    - stream: 0
+      offset: 0
+      format: 0
+      dimension: 0
+    - stream: 0
+      offset: 0
+      format: 0
+      dimension: 0
+    - stream: 0
+      offset: 0
+      format: 0
+      dimension: 0
+    - stream: 0
+      offset: 0
+      format: 0
+      dimension: 0
+    - stream: 0
+      offset: 0
+      format: 0
+      dimension: 0
+    - stream: 0
+      offset: 0
+      format: 0
+      dimension: 0
+    - stream: 0
+      offset: 0
+      format: 0
+      dimension: 0
+    - stream: 0
+      offset: 0
+      format: 0
+      dimension: 0
+    - stream: 0
+      offset: 0
+      format: 0
+      dimension: 0
+    - stream: 0
+      offset: 0
+      format: 0
+      dimension: 0
+    - stream: 0
+      offset: 0
+      format: 0
+      dimension: 0
+    m_DataSize: 96
+    _typelessdata: 000080bf000080bf000080bf000080bf000080bf0000803f000080bf0000803f000080bf000080bf0000803f0000803f0000803f000080bf000080bf0000803f000080bf0000803f0000803f0000803f000080bf0000803f0000803f0000803f
+  m_CompressedMesh:
+    m_Vertices:
+      m_NumItems: 0
+      m_Range: 0
+      m_Start: 0
+      m_Data: 
+      m_BitSize: 0
+    m_UV:
+      m_NumItems: 0
+      m_Range: 0
+      m_Start: 0
+      m_Data: 
+      m_BitSize: 0
+    m_Normals:
+      m_NumItems: 0
+      m_Range: 0
+      m_Start: 0
+      m_Data: 
+      m_BitSize: 0
+    m_Tangents:
+      m_NumItems: 0
+      m_Range: 0
+      m_Start: 0
+      m_Data: 
+      m_BitSize: 0
+    m_Weights:
+      m_NumItems: 0
+      m_Data: 
+      m_BitSize: 0
+    m_NormalSigns:
+      m_NumItems: 0
+      m_Data: 
+      m_BitSize: 0
+    m_TangentSigns:
+      m_NumItems: 0
+      m_Data: 
+      m_BitSize: 0
+    m_FloatColors:
+      m_NumItems: 0
+      m_Range: 0
+      m_Start: 0
+      m_Data: 
+      m_BitSize: 0
+    m_BoneIndices:
+      m_NumItems: 0
+      m_Data: 
+      m_BitSize: 0
+    m_Triangles:
+      m_NumItems: 0
+      m_Data: 
+      m_BitSize: 0
+    m_UVInfo: 0
+  m_LocalAABB:
+    m_Center: {x: 0, y: 0, z: 0}
+    m_Extent: {x: 1, y: 1, z: 1}
+  m_MeshUsageFlags: 0
+  m_BakedConvexCollisionMesh: 
+  m_BakedTriangleCollisionMesh: 
+  m_MeshMetrics[0]: 1
+  m_MeshMetrics[1]: 1
+  m_MeshOptimizationFlags: 1
+  m_StreamData:
+    offset: 0
+    size: 0
+    path: