Fix crash when a chat channel references an invalid chat action set

When there are no chat action sets or an action set has been deleted, bad
things would happen (e.g. segfault) when listing chat channels.

src/sbbs3/scfg/scfgchat.c

@@ -324,7 +324,7 @@ void chan_cfg()
 			sprintf(opt[k++],"%-27.27s%s","Channel Guru"
 				,cfg.chan[i]->guru<cfg.total_gurus ? cfg.guru[cfg.chan[i]->guru]->name : "");
 			sprintf(opt[k++],"%-27.27s%s","Channel Action Set"
-				,cfg.actset[cfg.chan[i]->actset]->name);
+				,cfg.chan[i]->actset < cfg.total_actsets ? cfg.actset[cfg.chan[i]->actset]->name : "INVALID!");
 			opt[k][0]=0;
 			uifc.helpbuf=
 				"`Chat Channel Configuration:`\n"