Query filter block: Restrict key handling to only when the modal is open

Previously, the key handler would try to run when the button was focused, but the modal was closed. Without having focusable elements set, this would cause the tab & shift+tab behavior to break. Restricting to the open modal keeps the focus-trap working when open.

Fixes #471

mu-plugins/blocks/query-filter/src/view.js

@@ -87,6 +87,11 @@ const { actions } = store( 'wporg/query-filter', {
 		},
 		handleKeydown: ( event ) => {
 			const context = getContext();
+			// Only handle key events if the dropdown is open.
+			if ( ! context.isOpen ) {
+				return;
+			}
+
 			// If Escape close the dropdown.
 			if ( event.key === 'Escape' ) {
 				actions.closeDropdown();