mailinfo: remove calls to exit() and die() deep in the callchain

The top-level mailinfo() would instead punt when the code in the
deeper part of the callchain detects an unrecoverable error in the
input.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

mailinfo.h

@@ -31,6 +31,7 @@ struct mailinfo {
 	struct strbuf **s_hdr_data;
 
 	struct strbuf log_message;
+	int input_error;
 };
 
 extern void setup_mailinfo(struct mailinfo *);