Bug 1020439 - Call cairo_surface_destroy in GetCairoSurfaceForSourceSurface in case of failure. r=bas

gfx/2d/DrawTargetCairo.cpp

@@ -177,6 +177,7 @@ GetCairoSurfaceForSourceSurface(SourceSurface *aSurface, bool aExistingOnly = fa
   // investigation hasn't been done to determine the underlying cause.  We
   // will just handle the failure to allocate the surface to avoid a crash.
   if (cairo_surface_status(surf)) {
+    cairo_surface_destroy(surf);
     return nullptr;
   }