x11: don't grab the pointer while buttons are pressed

Grabbing the mouse interrupts touch events in progress, so if someone
enables relative mode while a button is pressed, wait for the button to
be released before grabbing the mouse.

src/video/x11/SDL_x11events.c

@@ -1180,6 +1180,10 @@ void X11_HandleButtonRelease(SDL_VideoDevice *_this, SDL_WindowData *windowdata,
             button -= (8 - SDL_BUTTON_X1);
         }
         SDL_SendMouseButton(timestamp, window, mouseID, button, false);
+
+        if (window->internal->pending_grab) {
+            X11_SetWindowMouseGrab(_this, window, true);
+        }
     }
 }
 

src/video/x11/SDL_x11window.c

@@ -2058,6 +2058,7 @@ bool X11_SetWindowMouseGrab(SDL_VideoDevice *_this, SDL_Window *window, bool gra
         return SDL_SetError("Invalid window data");
     }
     data->mouse_grabbed = false;
+    data->pending_grab = false;
 
     display = data->videodata->display;
 
@@ -2075,7 +2076,8 @@ bool X11_SetWindowMouseGrab(SDL_VideoDevice *_this, SDL_Window *window, bool gra
          * the confinement grab.
          */
         if (data->xinput2_mouse_enabled && SDL_GetMouseState(NULL, NULL)) {
-            X11_XUngrabPointer(display, CurrentTime);
+            data->pending_grab = true;
+            return true;
         }
 
         // Try to grab the mouse

src/video/x11/SDL_x11window.h

@@ -118,6 +118,7 @@ struct SDL_WindowData
     bool was_shown;
     bool emit_size_move_after_property_notify;
     SDL_HitTestResult hit_test_result;
+    bool pending_grab;
 
     XPoint xim_spot;
     char *preedit_text;