Fixed crash getting clipboard data processing clipboard events on X11

SDL_PumpEvents() was freeing the temporary memory in the clipboard event, so if the application was iterating over the mime types in the event and retrieving the clipboard data, it would crash after the first entry.

(cherry picked from commit 3c0a6c32d4a35b8030f54d84f6ee8e8badf0f4f9)

src/video/x11/SDL_x11clipboard.c

@@ -139,7 +139,7 @@ static bool WaitForSelection(SDL_VideoDevice *_this, Atom selection_type, bool *
     waitStart = SDL_GetTicks();
     *flag = true;
     while (*flag) {
-        SDL_PumpEvents();
+        X11_PumpEvents(_this);
         waitElapsed = SDL_GetTicks() - waitStart;
         // Wait one second for a selection response.
         if (waitElapsed > 1000) {