Fix crash with MAIL env variable

src/mail.c

@@ -90,7 +90,12 @@ free_maildata()
 void
 getmailstatus()
 {
-    if (!mailbox && !(mailbox = nh_getenv("MAIL"))) {
+    char *emailbox;
+    if (emailbox = nh_getenv("MAIL")) {
+        mailbox = (char *) alloc((unsigned) strlen(emailbox));
+        Strcpy(mailbox, emailbox);
+    }
+    if (!mailbox) {
 #ifdef MAILPATH
 #ifdef AMS
         struct passwd ppasswd;