Windows: Handle absolute paths in safe_create_leading_directories().

In this function we must be careful to handle drive-local paths else there
is a danger that it runs into an infinite loop.

Signed-off-by: Johannes Sixt <johannes.sixt@telecom.at>

sha1_file.c

@@ -83,14 +83,18 @@ int get_sha1_hex(const char *hex, unsigned char *sha1)
 	return 0;
 }
 
+static inline int offset_1st_component(const char *path)
+{
+	if (has_dos_drive_prefix(path))
+		return 2 + (path[2] == '/');
+	return *path == '/';
+}
+
 int safe_create_leading_directories(char *path)
 {
-	char *pos = path;
+	char *pos = path + offset_1st_component(path);
 	struct stat st;
 
-	if (is_absolute_path(path))
-		pos++;
-
 	while (pos) {
 		pos = strchr(pos, '/');
 		if (!pos)