Fix SIGHUP handling by unconnected bgworkers

Add a SignalUnconnectedWorkers() call so that non-database-connected background
workers are also notified when postmaster is SIGHUPped.  Previously, only
database-connected workers were.

Michael Paquier (bug report and fix)

src/backend/postmaster/postmaster.c

@@ -2280,6 +2280,7 @@ SIGHUP_handler(SIGNAL_ARGS)
 				(errmsg("received SIGHUP, reloading configuration files")));
 		ProcessConfigFile(PGC_SIGHUP);
 		SignalChildren(SIGHUP);
+		SignalUnconnectedWorkers(SIGHUP);
 		if (StartupPID != 0)
 			signal_child(StartupPID, SIGHUP);
 		if (BgWriterPID != 0)