Ensure $delimiters is a string before trimming

src/Mustache/Tokenizer.php

@@ -107,7 +107,7 @@ class Mustache_Tokenizer
 
         $this->reset();
 
-        if ($delimiters = trim($delimiters)) {
+        if (is_string($delimiters) && $delimiters = trim($delimiters)) {
             $this->setDelimiters($delimiters);
         }