Bug with inline if-else and tuples

[gregdingle]

Thanks for all the work with mypy. I'm really enjoying it every time I code now.

I found this oddity which may be a bug.

Here is a short demo.

from typing import Tuple

def demo() -> Tuple[str, ...]:
    matches = [('a', 'b')]
    return matches[0] if matches else tuple()
    # demo.py:6: error: Incompatible return value type (got "object", expected "Tuple[str, ...]")


def noerror() -> Tuple[str, ...]:
    matches = [('a', 'b')]
    if matches:
        return matches[0]
    else:
        return tuple()

[srittau]

Possibly related to #5392.

[ilevkivskyi]

This is just a combination of #4975 and #5392. Fixing any of those fill fix this as well.