Perform pending destroys before unlocking the submit mutex (#28)

This makes the order of VULKAN_Submit consistent with VULKAN_Wait.

Co-authored-by: Caleb Cornett <caleb.cornett@outlook.com>
Reviewed-on: MoonsideGames/Refresh#28
Co-authored-by: TheSpydog <thespydog@noreply.example.org>
Co-committed-by: TheSpydog <thespydog@noreply.example.org>

src/Refresh_Driver_Vulkan.c

@@ -10038,11 +10038,11 @@ static void VULKAN_Submit(
 		}
 	}
 
-	SDL_UnlockMutex(renderer->submitLock);
-
 	/* Check pending destroys */
 
 	VULKAN_INTERNAL_PerformPendingDestroys(renderer);
+
+	SDL_UnlockMutex(renderer->submitLock);
 }
 
 /* Device instantiation */