Avoid a crash on pasting files to text edits

The mime data object fed to qWasmClipboardPaste in qClipboardPasteTo
might have empty formats. We unconditionally check the first format
nevertheless, which leads to a crash. Avoid feeding empty mime data
to the widget system.

Fixes: QTBUG-108840
Change-Id: If874e973b742d35c16cb8a87194d9d4b8f470801
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>

src/plugins/platforms/wasm/qwasmclipboard.cpp

@@ -139,7 +139,8 @@ static void qClipboardPasteTo(val dataTransfer)
             } // next item
         }
     }
-    qWasmClipboardPaste(mMimeData);
+    if (!mMimeData->formats().isEmpty())
+        qWasmClipboardPaste(mMimeData);
 }
 
 EMSCRIPTEN_BINDINGS(qtClipboardModule) {