mailinfo: release strbuf on error return in handle_boundary()

Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

mailinfo.c

@@ -928,6 +928,7 @@ again:
 			error("Detected mismatched boundaries, can't recover");
 			mi->input_error = -1;
 			mi->content_top = mi->content;
+			strbuf_release(&newline);
 			return 0;
 		}
 		handle_filter(mi, &newline);