dir.c: squelch false uninitialized memory warning

GCC 4.4.4 on MacOS incorrectly warns about potential use of uninitialized memory.

Signed-off-by: Pat Notz <patnotz@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

dir.c

@@ -232,7 +232,7 @@ int add_excludes_from_file_to_list(const char *fname,
 {
 	struct stat st;
 	int fd, i;
-	size_t size;
+	size_t size = 0;
 	char *buf, *entry;
 
 	fd = open(fname, O_RDONLY);