~ use array_key_exists instead of isset

Signed-off-by: Christoph Potas <christoph286@googlemail.com>

system/Language/Language.php

@@ -152,7 +152,7 @@ protected function parseLine(string $line): array
 		$file = substr($line, 0, strpos($line, '.'));
 		$line = substr($line, strlen($file) + 1);
 
-		if (! isset( $this->language[$this->locale][$file] ) )
+		if (! array_key_exists( $line, $this->language[$this->locale][$file] ) )
 		{
 			$this->load($file, $this->locale);
 		}