GPU: Add missing error code to VkErrorMessages()

(cherry picked from commit 906c6c7516)

src/gpu/vulkan/SDL_gpu_vulkan.c

@@ -1255,6 +1255,7 @@ static inline const char *VkErrorMessages(VkResult code)
         ERR_TO_STR(VK_ERROR_FULL_SCREEN_EXCLUSIVE_MODE_LOST_EXT)
         ERR_TO_STR(VK_SUBOPTIMAL_KHR)
         ERR_TO_STR(VK_ERROR_NATIVE_WINDOW_IN_USE_KHR)
+        ERR_TO_STR(VK_ERROR_INVALID_SHADER_NV)
     default:
         return "Unhandled VkResult!";
     }