added missing else clause to avoid infinite loops

CHANGELOG

@@ -1,5 +1,6 @@
 * 1.35.3 (2018-XX-XX)
 
+ * added missing else clause to avoid infinite loops
  * fixed .. (range operator) in sandbox policy
 
 * 1.35.2 (2018-03-03)

lib/Twig/Lexer.php

@@ -343,6 +343,9 @@ class Twig_Lexer implements Twig_LexerInterface
 
             $this->popState();
             ++$this->cursor;
+        } else {
+            // unlexable
+            throw new Twig_Error_Syntax(sprintf('Unexpected character "%s".', $this->code[$this->cursor]), $this->lineno, $this->source);
         }
     }