x11: Always update clipboard owner

This allows utilities like clipboard managers to keep track of the
changes.

(cherry picked from commit 65aaf3a9ab)

src/video/x11/SDL_x11clipboard.c

@@ -132,10 +132,7 @@ static int SetSelectionText(_THIS, const char *text, Atom selection_type)
                         X11_GetSDLCutBufferClipboardInternalFormat(display, SDL_X11_CLIPBOARD_MIME_TYPE_STRING), 8, PropModeReplace,
                         (const unsigned char *)text, SDL_strlen(text));
 
-    if (X11_XGetSelectionOwner(display, selection_type) != window) {
+    X11_XSetSelectionOwner(display, selection_type, window, CurrentTime);
-        X11_XSetSelectionOwner(display, selection_type, window, CurrentTime);
-    }
-
     return 0;
 }