Merge branch 'jt/mailinfo-fold-in-body-headers' into maint

Fix for NDEBUG builds.

* jt/mailinfo-fold-in-body-headers:
  mailinfo.c: move side-effects outside of assert

mailinfo.c

@@ -710,7 +710,8 @@ static void flush_inbody_header_accum(struct mailinfo *mi)
 {
 	if (!mi->inbody_header_accum.len)
 		return;
-	assert(check_header(mi, &mi->inbody_header_accum, mi->s_hdr_data, 0));
+	if (!check_header(mi, &mi->inbody_header_accum, mi->s_hdr_data, 0))
+		die("BUG: inbody_header_accum, if not empty, must always contain a valid in-body header");
 	strbuf_reset(&mi->inbody_header_accum);
 }