[sailfishos][compositor] Reset CompositorOGL::mFrameInProgress when e…

…arly leaving ::BeginPaint.

If the size of the compositing surface is 0 and we ignore the BeginPaint
call we need to make sure mFrameInProgress is not left set to true. If
it is the next ::BeginFrame call will trigger an assertion failure.

gfx/layers/opengl/CompositorOGL.cpp

@@ -657,8 +657,10 @@ CompositorOGL::BeginFrame(const nsIntRegion& aInvalidRegion,
 
   // We can't draw anything to something with no area
   // so just return
-  if (width == 0 || height == 0)
+  if (width == 0 || height == 0) {
+    mFrameInProgress = false;
     return;
+  }
 
   // We're about to actually draw a frame.
   mFrameInProgress = true;