Redundant NULL check for 'exc' after dereference in ceval.c

Redundant comparison with a NULL value at
https://github.com/python/cpython/blob/2e1544fd2b0cd46ba93fc51e3cdd47f4781d7499/Python/ceval.c#L3193
for pointer 'exc', which was dereferenced at
https://github.com/python/cpython/blob/2e1544fd2b0cd46ba93fc51e3cdd47f4781d7499/Python/ceval.c#L3192


### Linked PRs
* gh-135162