Fixed issue where when a PHP error dumps an HTML stack trace in the middle of an attribute, mb_strtolower() halts proceedings due to the input being an int rather than a string, so the input is now cast.

Author: hexydec

src/htmldoc/tokens/tag.php

@@ -251,7 +251,7 @@ public function minify(array $minify) : void {
 			// lowercase attribute key
 			if ($minify['lowercase']) {
 				unset($attributes[$key]);
-				$key = mb_strtolower($key);
+				$key = mb_strtolower(strval($key));
 				$attributes[$key] = $value;
 			}