When parsing a comment near EOF, or a comment escaping the end
of an expression block, the lexer did end up in an infinite loop.

-- Expect stderr --
Syntax error: Expecting expression
In line 1, byte 9:

 `{{ // }}`
          ^-- Near here


-- End --

-- Testcase --
{{ // }}
-- End --


-- Expect stderr --
Syntax error: Unterminated comment
In line 1, byte 4:

 `{{ /* }}`
     ^-- Near here


-- End --

-- Testcase --
{{ /* }}
-- End --
