fix: Prevent using simplexml_load_file() on missing file #142

Job	Run time
PHP 7.4 \| WP 6.1 \| prefer-stable	4m 5s
PHP 7.4 \| WP 6.1 (MS) \| prefer-stable	4m 16s
PHP 7.4 \| WP latest \| prefer-stable	6m 6s
PHP 7.4 \| WP latest (MS) \| prefer-stable	4m 7s
PHP 7.4 \| WP trunk \| prefer-stable	4m 0s
PHP 8.1 \| WP trunk \| prefer-stable	6m 8s
PHP 8.0 \| WP latest \| prefer-stable	6m 9s
PHP 8.1 \| WP latest \| prefer-stable	4m 3s
PHP 7.4 (Imagick) \| WP latest \| prefer-stable	4m 4s
PHP 7.4 (with coverage) \| WP latest \| prefer-stable	4m 17s
	47m 15s

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