[PATCH] mailinfo: avoid segfault when can't open files

["Juan F. Codagnone" <jcodagnone@gmail.com>]

If <msg> or <patch> files can't be opened, clear_mailinfo crash as
it follows NULL pointers.

Can be reproduced using `git mailinfo . .`

Signed-off-by: Juan F. Codagnone <jcodagnone@gmail.com>
---
 mailinfo.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/mailinfo.c b/mailinfo.c
index a89db22ab..035abbbf5 100644
--- a/mailinfo.c
+++ b/mailinfo.c
@@ -1167,11 +1167,13 @@ void clear_mailinfo(struct mailinfo *mi)
 	strbuf_release(&mi->inbody_header_accum);
 	free(mi->message_id);
 
-	for (i = 0; mi->p_hdr_data[i]; i++)
-		strbuf_release(mi->p_hdr_data[i]);
+	if(mi->p_hdr_data != NULL)
+		for (i = 0; mi->p_hdr_data[i]; i++)
+			strbuf_release(mi->p_hdr_data[i]);
 	free(mi->p_hdr_data);
-	for (i = 0; mi->s_hdr_data[i]; i++)
-		strbuf_release(mi->s_hdr_data[i]);
+	if(mi->s_hdr_data != NULL)
+		for (i = 0; mi->s_hdr_data[i]; i++)
+			strbuf_release(mi->s_hdr_data[i]);
 	free(mi->s_hdr_data);
 
 	while (mi->content < mi->content_top) {
-- 
2.14.3