Setting a limit smaller than the minimum possible size of a regex raises ValueError instead of more specific error.

[jodukes]

Steps to reproduce:

>>> from xeger import Xeger
>>> Xeger(limit=1).xeger("a{2}")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/local/ANT/jodukes/.local/lib/python2.7/site-packages/xeger/xeger.py", line 82, in xeger
    result = self._build_string(parsed)
  File "/home/local/ANT/jodukes/.local/lib/python2.7/site-packages/xeger/xeger.py", line 89, in _build_string
    newstr.append(self._handle_state(state))
  File "/home/local/ANT/jodukes/.local/lib/python2.7/site-packages/xeger/xeger.py", line 94, in _handle_state
    return self._cases[str(opcode).lower()](value)
  File "/home/local/ANT/jodukes/.local/lib/python2.7/site-packages/xeger/xeger.py", line 71, in <lambda>
    'max_repeat': lambda x: self._handle_repeat(*x),
  File "/home/local/ANT/jodukes/.local/lib/python2.7/site-packages/xeger/xeger.py", line 113, in _handle_repeat
    times = randint(start_range, end_range)
  File "/usr/lib/python2.7/random.py", line 242, in randint
    return self.randrange(a, b+1)
  File "/usr/lib/python2.7/random.py", line 218, in randrange
    raise ValueError, "empty range for randrange() (%d,%d, %d)" % (istart, istop, width)
ValueError: empty range for randrange() (2,2, 0)

Expected behaviour:

I expect to see a specific warning that lets me know why the input was bad. For example, one could add assert start_range < end_range, "Character limit exceeded during repeat" before randint in Xeger._handle_repeat

[gatopeich]

This hits me too. The "default" limit should only apply to undefined ranges like .+ or .*.