[ui gtk] Fix init, resize and destroy

Prevent Vulkan Swap before display context is assigned.
Prevent resize while fullscreen (like in windows impl).
Use superclass Resize implementation to reduce code duplication.
Remove recursive call to GTKWindow::Close().
Destroy xcb window after superclass Close().
Set hwnd to null after closing on windows implementation.

src/xenia/gpu/vulkan/vulkan_graphics_system.cc

@@ -260,7 +260,7 @@ VulkanGraphicsSystem::CreateCommandProcessor() {
 }
 
 void VulkanGraphicsSystem::Swap(xe::ui::UIEvent* e) {
-  if (!command_processor_) {
+  if (!command_processor_ || !display_context_) {
     return;
   }