Better error reporting for video drivers with less than full functionality.

src/video/SDL_video.c

@@ -1339,6 +1339,10 @@ SDL_CreateWindowFrom(const void *data)
         SDL_UninitializedVideo();
         return NULL;
     }
+    if (!_this->CreateWindowFrom) {
+        SDL_Unsupported();
+        return NULL;
+    }
     window = (SDL_Window *)SDL_calloc(1, sizeof(*window));
     if (!window) {
         SDL_OutOfMemory();
@@ -1356,8 +1360,7 @@ SDL_CreateWindowFrom(const void *data)
     }
     _this->windows = window;
 
-    if (!_this->CreateWindowFrom ||
-        _this->CreateWindowFrom(_this, window, data) < 0) {
+    if (_this->CreateWindowFrom(_this, window, data) < 0) {
         SDL_DestroyWindow(window);
         return NULL;
     }
@@ -3181,11 +3184,13 @@ SDL_GetWindowWMInfo(SDL_Window * window, struct SDL_SysWMinfo *info)
     CHECK_WINDOW_MAGIC(window, SDL_FALSE);
 
     if (!info) {
+        SDL_InvalidParamError("info");
         return SDL_FALSE;
     }
     info->subsystem = SDL_SYSWM_UNKNOWN;
 
     if (!_this->GetWindowWMInfo) {
+        SDL_Unsupported();
         return SDL_FALSE;
     }
     return (_this->GetWindowWMInfo(_this, window, info));