Skip PostSubBuffer calls that have zero size.

src/libANGLE/Surface.cpp

@@ -230,6 +230,11 @@ Error Surface::postSubBuffer(const gl::Context *context,
                              EGLint width,
                              EGLint height)
 {
+    if (width == 0 || height == 0)
+    {
+        return egl::NoError();
+    }
+
     return mImplementation->postSubBuffer(context, x, y, width, height);
 }
 

src/libANGLE/renderer/gl/wgl/DXGISwapChainWindowSurfaceWGL.cpp

@@ -144,6 +144,7 @@ egl::Error DXGISwapChainWindowSurfaceWGL::postSubBuffer(const gl::Context *conte
                                                         EGLint width,
                                                         EGLint height)
 {
+    ASSERT(width > 0 && height > 0);
     ASSERT(mSwapChain1 != nullptr);
 
     mFunctionsGL->flush();