When editing a message, pass the proper to/from/subj/area to drop file

Fixes issue #704 - not just for JS bbs.edit_msg(), but for all uses of the underlying sbbs_t::editmsg() function.

Replaced one specific comparison of subnum == INVALID_SUB with call to is_valid_subnum() just to be consistent. No functional change there.

src/sbbs3/writemsg.cpp

@@ -589,7 +589,7 @@ bool sbbs_t::writemsg(const char *fname, const char *top, char *subj, int mode,
 				}
 			}
 		}
-		editor_inf(useron_xedit,to,from,subj,mode,subnum==INVALID_SUB ? nulstr : cfg.sub[subnum]->sname, tagfile);
+		editor_inf(useron_xedit,to,from,subj,mode, is_valid_subnum(subnum) ? cfg.sub[subnum]->sname : nulstr, tagfile);
 		if(cfg.xedit[useron_xedit-1]->type) {
 			gettimeleft();
 			xtrndat(mode&WM_ANON ? text[Anonymous]:from,cfg.node_dir,cfg.xedit[useron_xedit-1]->type
@@ -1664,7 +1664,7 @@ bool sbbs_t::editmsg(smb_t* smb, smbmsg_t *msg)
 	msg_tmp_fname(useron.xedit, msgtmp, sizeof(msgtmp));
 	(void)removecase(msgtmp);
 	msgtotxt(smb, msg, msgtmp, /* header: */false, /* mode: */is_msg ? GETMSGTXT_ALL : GETMSGTXT_BODY_ONLY);
-	if(!editfile(msgtmp, cfg.level_linespermsg[useron.level]))
+	if(!editfile(msgtmp, cfg.level_linespermsg[useron.level], msg->to, msg->from, msg->subj, is_valid_subnum(smb->subnum) ? cfg.sub[smb->subnum]->sname : nulstr))
 		return false;
 	length=(long)flength(msgtmp);
 	if(length<1L)