Fix iterator reset and add reset ranges

The `git_iterator_reset` command has not been working in all cases
particularly when there is a start and end range.  This fixes it
and adds tests for it, and also extends it with the ability to
update the start/end range strings when an iterator is reset.

1 files changed, 3 insertions, 0 deletions

diff --git a/src/tree.c b/src/tree.c
index 944992fea..7f1b9feb1 100644
--- a/src/tree.c
+++ b/src/tree.c
@@ -301,6 +301,9 @@ int git_tree__prefix_position(git_tree *tree, const char *path)
 	struct tree_key_search ksearch;
 	size_t at_pos;
 
+	if (!path)
+		return 0;
+
 	ksearch.filename = path;
 	ksearch.filename_len = strlen(path);