IfElseTimedateNA: Finds time value that is not NA
In Blakemassey/baear: Functions for Bald Eagle Data Manipulation and Model Fitting

Examines two time columns, if one is NA, the other time is returned.

1	IfElseTimedateNA(df, col1, col2, result, default_tz, tz)

`df`	Dataframe of location data.
`col1`	Column name, column checked to if is NA. If not NA, then col1 is returned.
`col2`	Column name, if col1 is NA, then col2 is returned.
`result`	String, name of column to insert results. Default is "result".
`default_tz`	String, timezone that timedate reverts to, based on OS time.
`tz`	string, timezone of original data (may be different from default_tz).