b=348317, black (or other solid color) parts/boxes on certain web pages, r=me/stuart

gfx/src/thebes/nsThebesImage.cpp

@@ -344,6 +344,7 @@ nsThebesImage::Draw(nsIRenderingContext &aContext, nsIDrawingSurface *aSurface,
 
         // otherwise
         ctx->SetColor(mSinglePixelColor);
+        ctx->NewPath();
         ctx->Rectangle(gfxRect(aDX, aDY, aDWidth, aDHeight), PR_TRUE);
         ctx->Fill();
         return NS_OK;