Exception during flight.query_ehs() related to Traffic indexing

[xoolive]

Using commit ccc46c4, upon calling:

ext_flight = flight.query_ehs()

Got one of the following exceptions:

File "[...]\traffic\core\flight.py", line 376, in query_ehs
        flight = t[self.callsign]
File "[...]\traffic\core\traffic.py", line 123, in __getitem__
        subset = list(index)  # noqa: F841

TypeError: 'int' object is not iterable
TypeError: 'float' object is not iterable

[xoolive]

• The float exception seems to be related to NaN values in the callsign column appearing during preprocessing when all last_position values are NaN.
• The int exception seems to be related to seldom cases when callsigns are being parsed as integers from the Impala cache.