notes: clean up confusing NULL checks in init_notes()

Coverity complains that we check whether "notes_ref" is NULL, but it was
already implied to be non-NULL earlier in the function. And this is
true; since b9342b3 (refs: add array of ref namespaces, 2022-08-05),
we call xstrdup(notes_ref) unconditionally, which would segfault if it
was NULL.

But that commit is actually doing the right thing. Even if NULL is
passed into the function, we'll use default_notes_ref() as a fallback,
which will never return NULL (it tries a few options, but its last
resort is a string literal). Ironically, the "!notes_ref" check was
added by the same commit that added the fallback: 709f79b (Notes
API: init_notes(): Initialize the notes tree from the given notes ref,
2010-02-13). So this check never did anything.

Signed-off-by: Jeff King <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: peff

notes.c

@@ -1019,13 +1019,13 @@ void init_notes(struct notes_tree *t, const char *notes_ref,
 	t->root = (struct int_node *) xcalloc(1, sizeof(struct int_node));
 	t->first_non_note = NULL;
 	t->prev_non_note = NULL;
-	t->ref = xstrdup_or_null(notes_ref);
+	t->ref = xstrdup(notes_ref);
 	t->update_ref = (flags & NOTES_INIT_WRITABLE) ? t->ref : NULL;
 	t->combine_notes = combine_notes;
 	t->initialized = 1;
 	t->dirty = 0;
 
-	if (flags & NOTES_INIT_EMPTY || !notes_ref ||
+	if (flags & NOTES_INIT_EMPTY ||
 	    repo_get_oid_treeish(the_repository, notes_ref, &object_oid))
 		return;
 	if (flags & NOTES_INIT_WRITABLE && read_ref(notes_ref, &object_oid))