Don't fill non-renderable background rects

There is a check for the background color painting border
being renderable (for rounded corners) but the check is
overlooked for the image rect. Fix that by treating the
image fill rect the same way we treat the color rect.

Bug: 1101080
Change-Id: I4328357f41793d00002cb80d27bd7182d1756be7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2283775
Commit-Queue: Stephen Chenney <schenney@chromium.org>
Reviewed-by: Fredrik Söderquist <fs@opera.com>
Cr-Commit-Position: refs/heads/master@{#786048}

third_party/blink/renderer/core/paint/box_painter_base.cc

@@ -567,6 +567,7 @@ inline bool PaintFastBottomLayer(Node* node,
     // clipping.
     clipper.emplace(context, rect, color_border);
     color_border.SetRadii(FloatRoundedRect::Radii());
+    image_border.SetRadii(FloatRoundedRect::Radii());
   }
 
   // Paint the color if needed.