strip_whitespace=True raises IndexError on "( AS )"

[andidukaj-beep]

sqlparse.format(sql, strip_whitespace=True) raises an unhandled IndexError for the input "( AS )" (a parenthesis group that ends up with fewer than two tokens). A parsing/formatting call should either handle the input or raise a clear parse error, not fail with list index out of range.

Version: reproduced on current master (commit 60cdc64).

Minimal reproducer:

import sqlparse
sqlparse.format("( AS )", strip_whitespace=True)

Traceback:

Traceback (most recent call last):
  (reproducer above)
    import sqlparse; sqlparse.format('( AS )', strip_whitespace=True)
                     ~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "sqlparse/__init__.py", line 60, in format
    return "".join(stack.run(sql, encoding))
           ~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "sqlparse/engine/filter_stack.py", line 44, in run
    filter_.process(stmt)
    ~~~~~~~~~~~~~~~^^^^^^
  File "sqlparse/filters/others.py", line 126, in process
    [self.process(sgroup, depth + 1) for sgroup in stmt.get_sublists()]
     ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^
  File "sqlparse/filters/others.py", line 127, in process
    self._stripws(stmt)
    ~~~~~~~~~~~~~^^^^^^
  File "sqlparse/filters/others.py", line 88, in _stripws
    func(tlist)
    ~~~~^^^^^^^
  File "sqlparse/filters/others.py", line 115, in _stripws_parenthesis
    while tlist.tokens[1].is_whitespace:
          ~~~~~~~~~~~~^^^
IndexError: list index out of range

Cause (from the traceback): _stripws_parenthesis accesses tlist.tokens[1] (and later tokens[-2]) without checking the group length; a parenthesis group with fewer than 2 tokens triggers the IndexError.

Expected: the input is parsed/formatted, or a clear parse error is raised — not an unhandled IndexError.