[BUGFIX] Fixes error when default language constant is empty

This is the error message:
"Warning: htmlspecialchars() expects parameter 1 to be string, array given in /var/www/ay.dev/typo3_src-patched/typo3/sysext/fluid/Classes/ViewHelpers/Form/TextareaViewHelper.php on line 65"

Classes/Service/FileBaseXLFService.php

@@ -57,6 +57,12 @@ class FileBaseXLFService extends FileBaseService {
 	public function readFile() {
 		$this->readXlfFile();
 
+		foreach ($this->localLang['default'] as $constant => $value) {
+			if (empty($value)) {
+				$this->localLang['default'][$constant] = '';
+			}
+		}
+
 		// convert all language values from utf-8 to the original charset
 		if (!Typo3Lib::isTypo3BackendInUtf8Mode()) {
 			$this->localLang = Typo3Lib::utf8($this->localLang, FALSE, array('default'));