Add a function `QVk_CheckExtent()` to query the extent state.

This will be used to detect if we've got an extent size of 0x0 because
the window has been maximized.

src/client/refresh/vk/header/qvk.h

@@ -315,6 +315,7 @@ void		QVk_DrawTexRect(const float *ubo, VkDeviceSize uboSize, qvktexture_t *text
 void		QVk_BindPipeline(qvkpipeline_t *pipeline);
 void		QVk_SubmitStagingBuffers(void);
 void		Qvk_MemoryBarrier(VkCommandBuffer cmdBuffer, VkPipelineStageFlags srcStageMask, VkPipelineStageFlags dstStageMask, VkAccessFlags srcAccessMask, VkAccessFlags dstAccessMask);
+qboolean	QVk_CheckExtent(void);
 
 // debug label related functions
 void		QVk_DebugSetObjectName(uint64_t obj, VkObjectType objType, const char *objName);

src/client/refresh/vk/vk_swapchain.c

@@ -127,6 +127,19 @@ static VkCompositeAlphaFlagBitsKHR getSupportedCompositeAlpha(VkCompositeAlphaFl
 	return VK_COMPOSITE_ALPHA_INHERIT_BIT_KHR;
 }
 
+qboolean QVk_CheckExtent(void)
+{
+	VkSurfaceCapabilitiesKHR surfaceCaps;
+	VK_VERIFY(vkGetPhysicalDeviceSurfaceCapabilitiesKHR(vk_device.physical, vk_surface, &surfaceCaps));
+
+	if (surfaceCaps.currentExtent.width == 0 || surfaceCaps.currentExtent.height == 0)
+	{
+		return false;
+	}
+
+	return true;
+}
+
 VkResult QVk_CreateSwapchain()
 {
 	VkSurfaceCapabilitiesKHR surfaceCaps;