pgsql: Avoid race during buffer fill/read.

lib/modules/Sql.pmod/pgsql_util.pmod

@@ -174,6 +174,7 @@ class conxiin {
     if(fillread) {
       array cid=callout(gottimeout,timeout);
       Thread.MutexKey lock=fillreadmux->lock();
+      if(!sizeof(this))
         fillread.wait(lock);
       lock=0;
       local_backend->remove_call_out(cid);