xwayland: prevent infinite event loop in XWM clipboard transfers (#11427)

Only recreate event source when onWrite() returns 1 (needs continuation).
Prevents infinite loop when no valid transfers are available, fixing high
CPU usage and error spam.

src/xwayland/XWM.cpp

@@ -1287,7 +1287,10 @@ void CXWM::getTransferData(SXSelection& sel) {
     }
 
     const size_t transferIndex = std::distance(sel.transfers.begin(), it);
-    sel.onWrite();
+    int          writeResult   = sel.onWrite();
+
+    if (writeResult != 1)
+        return;
 
     if (transferIndex >= sel.transfers.size())
         return;