Fix TypeError in ImageModal when file does not exist

The ImageBeforeProduceHTML hook passes File|false for the $file
parameter. When a page references a non-existent file, $file is false.
ImageModal::__construct() has a strict File type hint, causing a
TypeError.

Add a guard to skip modal replacement when the file does not exist,
letting MediaWiki render its normal missing-file link instead.

Bug: #71

Author: kghbln

src/HooksHandler.php

@@ -140,6 +140,9 @@ public function onImageBeforeProduceHTML(
 	): bool {
 		if ( $this->getConfig()->has( 'BootstrapComponentsModalReplaceImageTag' ) &&
 			$this->getConfig()->get( 'BootstrapComponentsModalReplaceImageTag' ) ) {
+			if ( !$file ) {
+				return true;
+			}
 			$imageModal = new ImageModal( $linker, $title, $file,
 				$this->getNestingController(), $this->getBootstrapComponentsService()
 			);