(ins_from_clip): fix maybe-uninitialized warning.

../../../lib/widget/input.c:573:8: error: 'event_data.ret' may be used uninitialized [-Werror=maybe-uninitialized]
  573 |     if (event_data.ret)
      |        ^
../../../lib/widget/input.c:566:35: note: 'event_data.ret' was declared here
  566 |     ev_clipboard_text_from_file_t event_data;

Found by gcc-11.

Signed-off-by: Andreas Mohr <and@gmx.li>
Signed-off-by: Andrew Borodin <aborodin@vmail.ru>

lib/widget/input.c

@@ -561,7 +561,7 @@ static void
 ins_from_clip (WInput * in)
 {
     char *p = NULL;
-    ev_clipboard_text_from_file_t event_data;
+    ev_clipboard_text_from_file_t event_data = { NULL, FALSE };
 
     /* try use external clipboard utility */
     mc_event_raise (MCEVENT_GROUP_CORE, "clipboard_file_from_ext_clip", NULL);