cmdutils: Use 64bit for file size/offset related variable in cmdutils_read_file()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 369b4cd4)
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

cmdutils.c

@@ -1860,7 +1860,7 @@ int read_yesno(void)
 
 int cmdutils_read_file(const char *filename, char **bufptr, size_t *size)
 {
-    int ret;
+    int64_t ret;
     FILE *f = av_fopen_utf8(filename, "rb");
 
     if (!f) {