Fix changes to author/committer not saved

Prior to this, when editing a changeset, the only change that was
actually applied was when resetting author/committer to the original
value from source control (i.e. selecting '--' from the list). Other
values were not saved.

This was due to use of user_ensure_exists(), which always returns void.

Fixes #163

Author: dregad

Source/pages/edit.php

@@ -24,11 +24,11 @@
 $t_repo = array_shift( $t_repos );
 $t_repo->load_branches();
 
-if ( $f_user_id == 0 || user_ensure_exists( $f_user_id ) ) {
+if ( $f_user_id == 0 || user_exists( $f_user_id ) ) {
 	$t_changeset->user_id = $f_user_id;
 }
 
-if ( $f_committer_id == 0 || user_ensure_exists( $f_committer_id ) ) {
+if ( $f_committer_id == 0 || user_exists( $f_committer_id ) ) {
 	$t_changeset->committer_id = $f_committer_id;
 }