Insure the WM_EMAIL mode flag is set when calling writemsg() from email()

- similar to what we do in netmail() with the WM_NETMAIL flag.
If you call writemsg() without WM_EMAIL set, it tries to use the subnum as an
index into the sub-board array and will crash.

src/sbbs3/email.cpp

@@ -121,7 +121,7 @@ bool sbbs_t::email(int usernumber, const char *top, const char *subj, long mode)
 
 	msg_tmp_fname(useron.xedit, msgpath, sizeof(msgpath));
 	username(&cfg,usernumber,str2);
-	if(!writemsg(msgpath,top, /* subj: */title,mode,INVALID_SUB,/* to: */str2,/* from: */useron.alias, &editor)) {
+	if(!writemsg(msgpath,top, /* subj: */title,WM_EMAIL|mode,INVALID_SUB,/* to: */str2,/* from: */useron.alias, &editor)) {
 		bputs(text[Aborted]);
 		return(false); 
 	}