message: fix minor issues
  use the clear flags to skip the clear code earlier
  better detection of the msaa RenderTarger with non msaa attachments
diff: @@ -2173,7 +2173,7 @@ void OpenGLDriver::beginRenderPass(Handle<HwRenderTarget> rth,
  }
  }
  - if (rt->gl.fbo_read != rt->gl.fbo) {
  + if (rt->gl.fbo_read) {
  // we have a multi-sample RenderTarget with non multi-sample attachments (i.e. this is the
  // EXT_multisampled_render_to_texture emulation).
  // We need to perform a "backward" resolve, i.e. load the resolved texture into the tile,
  @@ -2197,6 +2197,7 @@ void OpenGLDriver::beginRenderPass(Handle<HwRenderTarget> rth,
  setScissor(params.viewport.left, params.viewport.bottom,
  params.viewport.width, params.viewport.height);
  + if (clearFlags & TargetBufferFlags::ALL) {
  const bool respectScissor = !(clearFlags & RenderPassFlags::IGNORE_SCISSOR);
  const bool clearColor = clearFlags & TargetBufferFlags::COLOR;
  const bool clearDepth = clearFlags & TargetBufferFlags::DEPTH;
  @@ -2218,6 +2219,7 @@ void OpenGLDriver::beginRenderPass(Handle<HwRenderTarget> rth,
  clearDepth, params.clearDepth,
  clearStencil, params.clearStencil);
  }
  + }
  #ifndef NDEBUG
  // clear the discarded (but not the cleared ones) buffers in debug builds
  