Type inference regression with "and" and strict optional disabled

[JukkaL]

This generates a false positive:

# mypy: no-strict-optional
from typing import Tuple, Dict, Optional, NamedTuple

class C(NamedTuple):
    x: int

t: Optional[C]

d: Dict[C, bytes]

x = t and d[t]
if x:
    x.startswith(b'x')  # Item "C" of "Union[C, bytes]" has no attribute "startswith"

It started happening as a side effect of #10389.

This is a regression, so this may be high priority. However, since this only seems to happen when strict optional checking is disabled, the impact may be pretty minor.

cc @ethan-leba

[sobolevn]

The problem is that t and d[t] is revealed as Union[Tuple[builtins.int, fallback=ex.C], builtins.bytes*]. But, it should be revealed as Optional[bytes]

I will try to solve it.

[sobolevn]

Let's test it: #11717