Bug #20304 mysqltest: reap with no preceding statement hangs forever

Added sanity check, similar to the one preventing send without reap

client/mysqltest.cc

@@ -7370,6 +7370,9 @@ void run_query(struct st_connection *cn, struct st_command *command, int flags)
   if (cn->pending && (flags & QUERY_SEND_FLAG))
     die ("Cannot run query on connection between send and reap");
 
+  if (!(flags & QUERY_SEND_FLAG) && !cn->pending)
+    die ("Cannot reap on a connection without pending send");
+  
   init_dynamic_string(&ds_warnings, NULL, 0, 256);
   /*
     Evaluate query if this is an eval command