Bug 1222123 - Warning fix in CompositorD3D11.cpp. r=Bas

gfx/layers/d3d11/CompositorD3D11.cpp

@@ -546,9 +546,7 @@ CompositorD3D11::CreateRenderTargetFromSource(const gfx::IntRect &aRect,
     const IntSize& srcSize = sourceD3D11->GetSize();
     MOZ_ASSERT(srcSize.width >= 0 && srcSize.height >= 0,
                "render targets should have nonnegative sizes");
-    if (srcBox.left >= 0 &&
-        srcBox.top >= 0 &&
-        srcBox.left < srcBox.right &&
+    if (srcBox.left < srcBox.right &&
         srcBox.top < srcBox.bottom &&
         srcBox.right <= static_cast<uint32_t>(srcSize.width) &&
         srcBox.bottom <= static_cast<uint32_t>(srcSize.height)) {