sha1_file: don't convert off_t to size_t too early to avoid potential die()

xsize_t() checks if an off_t argument can be safely converted to
a size_t return value.  If the check is executed too early, it could
fail for large files on 32-bit architectures even if the size_t code
path is not taken.  Other paths might be able to handle the large file.
Specifically, index_stream_convert_blob() is able to handle a large file
if a filter is configured that returns a small result.

Signed-off-by: Steffen Prohaska <prohaska@zib.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

sha1_file.c

@@ -3178,17 +3178,22 @@ int index_fd(unsigned char *sha1, int fd, struct stat *st,
 	     enum object_type type, const char *path, unsigned flags)
 {
 	int ret;
-	size_t size = xsize_t(st->st_size);
 
+	/*
+	 * Call xsize_t() only when needed to avoid potentially unnecessary
+	 * die() for large files.
+	 */
 	if (type == OBJ_BLOB && path && would_convert_to_git_filter_fd(path))
 		ret = index_stream_convert_blob(sha1, fd, path, flags);
 	else if (!S_ISREG(st->st_mode))
 		ret = index_pipe(sha1, fd, type, path, flags);
-	else if (size <= big_file_threshold || type != OBJ_BLOB ||
+	else if (st->st_size <= big_file_threshold || type != OBJ_BLOB ||
 		 (path && would_convert_to_git(path)))
-		ret = index_core(sha1, fd, size, type, path, flags);
+		ret = index_core(sha1, fd, xsize_t(st->st_size), type, path,
+				 flags);
 	else
-		ret = index_stream(sha1, fd, size, type, path, flags);
+		ret = index_stream(sha1, fd, xsize_t(st->st_size), type, path,
+				   flags);
 	close(fd);
 	return ret;
 }