Fix segfault on ppc when browsing tree

ui-blob.c

@@ -50,7 +50,7 @@ void cgit_print_blob(const char *hex, char *path, const char *head)
 		commit = lookup_commit_reference(sha1);
 		match_path = path;
 		matched_sha1 = sha1;
-		read_tree_recursive(commit->tree, NULL, 0, 0, paths, walk_tree, NULL);
+		read_tree_recursive(commit->tree, "", 0, 0, paths, walk_tree, NULL);
 		type = sha1_object_info(sha1,&size);
 	}
 

ui-plain.c

@@ -88,7 +88,7 @@ void cgit_print_plain(struct cgit_context *ctx)
 		return;
 	}
 	match_path = ctx->qry.path;
-	read_tree_recursive(commit->tree, NULL, 0, 0, paths, walk_tree, NULL);
+	read_tree_recursive(commit->tree, "", 0, 0, paths, walk_tree, NULL);
 	if (!match)
 		html_status(404, "Not found", 0);
 }

ui-tree.c

@@ -280,6 +280,6 @@ void cgit_print_tree(const char *rev, char *path)
 	}
 
 	match_path = path;
-	read_tree_recursive(commit->tree, NULL, 0, 0, paths, walk_tree, NULL);
+	read_tree_recursive(commit->tree, "", 0, 0, paths, walk_tree, NULL);
 	ls_tail();
 }