fast-import: do not clear notes in do_change_note_fanout()

Commit 5edde51 (fast-import: filemodify after M 040000 <tree> ""
crashes, 2010-10-17) taught fast-import to load trees from the
object db as needed when it is time to access them.

But it went too far.  In change_note_fanout(), an empty,
not-loaded tree is not meant to destroy notes, so calling
load_tree() at that point is exactly the wrong thing to do.

Kudos to Johan Herland for t9301, which caught this failure.

Reported-by: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

fast-import.c

@@ -2070,16 +2070,13 @@ static uintmax_t do_change_note_fanout(
 		char *fullpath, unsigned int fullpath_len,
 		unsigned char fanout)
 {
-	struct tree_content *t;
+	struct tree_content *t = root->tree;
 	struct tree_entry *e, leaf;
 	unsigned int i, tmp_hex_sha1_len, tmp_fullpath_len;
 	uintmax_t num_notes = 0;
 	unsigned char sha1[20];
 	char realpath[60];
 
-	if (!root->tree);
-		load_tree(root);
-	t = root->tree;
 	for (i = 0; t && i < t->entry_count; i++) {
 		e = t->entries[i];
 		tmp_hex_sha1_len = hex_sha1_len + e->name->str_len;