Fix a rounding error when detecting overflows

Fix #2100.

weasyprint/layout/__init__.py

@@ -245,9 +245,13 @@ def __init__(self, style_for, get_image_from_uri, font_config,
         self.dictionaries = {}
 
     def overflows_page(self, bottom_space, position_y):
+        return self.overflows(self.page_bottom - bottom_space, position_y)
+
+    @staticmethod
+    def overflows(bottom, position_y):
         # Use a small fudge factor to avoid floating numbers errors.
         # The 1e-9 value comes from PEP 485.
-        return position_y > (self.page_bottom - bottom_space) * (1 + 1e-9)
+        return position_y > bottom * (1 + 1e-9)
 
     def create_block_formatting_context(self):
         self.excluded_shapes = []

weasyprint/layout/block.py

@@ -742,7 +742,7 @@ def block_container_layout(context, box, bottom_space, skip_stack,
                 max_lines)
         elif stop:
             if box.height != 'auto':
-                if position_y > box.position_y + box.height:
+                if context.overflows(box.position_y + box.height, position_y):
                     # Box heigh is fixed and it doesn’t overflow page, forget
                     # overflowing children.
                     resume_at = None