Fix logic to match before and cast instead

Signed-off-by: Scott Kingsley Clark <scott@skc.dev>

classes/PodsUI.php

@@ -3000,7 +3000,7 @@ public function manage( $reorder = false ) {
 
 							echo PodsForm::submit_button( $this->header['search'], 'button', false, false, array( 'id' => $this->num_prefix . 'search' . $this->num . '-submit' ) );
 
-							if ( NULL === $this->search ) {
+							if ( 0 < strlen( (string) $this->search ) ) {
 								$clear_filters = array(
 									$this->num_prefix . 'search' . $this->num => false,
 								);