Fix a bug when tokenize an InfixExpression ends with a decimal number

[bytezzz]

A bug occurs when I was trying to tokenize an infixExpression ends with a decimal number, and I tried to fix this problem.

Python 3.10.4 (main, Jan 25 2023, 00:13:50) [GCC 9.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import javalang
>>> list(javalang.tokenizer.tokenize('a == 0'))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/workspaces/javalang/javalang/tokenizer.py", line 538, in tokenize
    token_type = self.read_integer_or_float(c, c_next)
  File "/workspaces/javalang/javalang/tokenizer.py", line 370, in read_integer_or_float
    if c == '0' and c_next in 'xX':
TypeError: 'in <string>' requires string as left operand, not NoneType

[JoachimCoenen]

This happens only for the single-digit decimal integer '0'?

[bytezzz]

Sorry, It has been a long time and I can't remember it.