Fixing issue #1187 (#1206)

* Passing null to SkPathMeasure results in AccessViolationException

Co-authored-by: Ziriax <[email protected]>

binding/Binding/SKPathMeasure.cs

@@ -19,8 +19,13 @@ public SKPathMeasure ()
 		}
 
 		public SKPathMeasure (SKPath path, bool forceClosed = false, float resScale = 1)
-			: this (SkiaApi.sk_pathmeasure_new_with_path (path == null ? IntPtr.Zero : path.Handle, forceClosed, resScale), true)
+			: this (IntPtr.Zero, true)
 		{
+			if (path == null)
+				throw new ArgumentNullException (nameof (path));
+
+			Handle = SkiaApi.sk_pathmeasure_new_with_path (path.Handle, forceClosed, resScale);
+
 			if (Handle == IntPtr.Zero) {
 				throw new InvalidOperationException ("Unable to create a new SKPathMeasure instance.");
 			}

tests/Tests/SKPathMeasureTest.cs

@@ -0,0 +1,30 @@
+using System;
+using Xunit;
+
+namespace SkiaSharp.Tests
+{
+	public class SKPathMeasureTest : SKTest
+	{
+		[SkippableFact]
+		public void ConstructorThrowsOnNullPathArgument()
+		{
+			var ex = Assert.Throws<ArgumentNullException>(() => new SKPathMeasure(null));
+			Assert.Equal("path", ex.ParamName);
+		}
+
+		[SkippableFact]
+		public void ConstructorDoesNotThrownOnNonNullPathArgument()
+		{
+			var path = new SKPath();
+			var pm = new SKPathMeasure(path);
+			Assert.NotNull(pm);
+		}
+
+		[SkippableFact]
+		public void EmptyConstructorDoesNotThrow()
+		{
+			var pm = new SKPathMeasure();
+			Assert.NotNull(pm);
+		}
+	}
+}