GetClientRect() fails on closed hwnd which left the rectangle uninitialized and copied to DisplaySize. Ensure it is zero + similar failsafe in io.WantSetMousePos path.
This allows for binding the pipeline/sending draw commands
(via `ImGui_ImplVulkan_RenderDrawData`) against any subpass, rather than
being restricted to only the first subpass.
Without this, attempting to bind the pipeline against a subpass other than
the first one results in validation layer errors and, at worst, some drivers
failing if the subpass attachments differ.