improve file_from_env script

Signed-off-by: Benjamin Brahmer <info@b-brahmer.de>

bin/tools/file_from_env.php

@@ -13,12 +13,17 @@
 if ($argc < 2) {
     echo "This script expects two parameters:\n";
     echo "./file_from_env.php ENV_VAR PATH_TO_FILE\n";
-    exit;
+    exit(1);
 }
 
 # Read environment variable
 $content = getenv($argv[1]);
 
+if (!$content){
+    echo "Variable was empty\n";
+    exit(1);
+}
+
 file_put_contents($argv[2], $content);
 
 echo "Done...\n";