Fix omemo autocompletion mitake

Don't return too early. We still need to check for regular omemo
autocompletion (omemo_ac).

src/command/cmd_ac.c

@@ -2399,8 +2399,6 @@ _omemo_autocomplete(ProfWin *window, const char *const input, gboolean previous)
                     }
                 }
             }
-
-            return NULL;
         }
 #endif
     }