Bug 539356 - Part 23 - Fix MovePixels crash when our surface is in an error state. r=jrmuizel

gfx/thebes/gfxASurface.cpp

@@ -488,6 +488,13 @@ gfxASurface::MovePixels(const nsIntRect& aSourceRect,
     nsRefPtr<gfxASurface> tmp = 
       CreateSimilarSurface(GetContentType(), 
                            gfxIntSize(aSourceRect.width, aSourceRect.height));
+    // CreateSimilarSurface can return nsnull if the current surface is
+    // in an error state. This isn't good, but its better to carry
+    // on with the error surface instead of crashing.
+    NS_ASSERTION(tmp, "Must have temporary surface to move pixels!");
+    if (!tmp) {
+        return;
+    }
     nsRefPtr<gfxContext> ctx = new gfxContext(tmp);
     ctx->SetOperator(gfxContext::OPERATOR_SOURCE);
     ctx->SetSource(this, gfxPoint(-aSourceRect.x, -aSourceRect.y));