Python: False positive in python/Statements/UnreachableCode

[Anthchirp]

Example:
https://lgtm.com/projects/g/dials/data/snapshot/5649de308532bce681716dc8235a851850c93bcd/files/dials_data/download.py#x29a04cee487f283d:1

In the snippet

try:
  import fcntl
except ImportError:
  pass

the except path is incorrectly identified as unreachable code. fcntl is a standard library module, but not present on Python for Windows.

[ndevenish]

To add to this; I'm also seeing this in some code that looks like:

try:
    import __builtin__
except ImportError:
    import builtins as __builtin__

This was written because __builtin__ doesn't exist on python3.