Bug 1372870 - Compiling with mingw-w64 based on GCC 6.3.0 breaks (operands to ?: have different types) r=mattwoodrow

gfx/layers/d3d11/TextureD3D11.h

@@ -239,7 +239,7 @@ public:
   virtual ID3D11ShaderResourceView* GetShaderResourceView() override;
 
   // Returns nullptr if this texture was created by a DXGI TextureHost.
-  virtual DataTextureSource* AsDataTextureSource() override { return mAllowTextureUploads ? this : false; }
+  virtual DataTextureSource* AsDataTextureSource() override { return mAllowTextureUploads ? this : nullptr; }
 
   virtual void DeallocateDeviceData() override { mTexture = nullptr; }