bw_custom_column_admin() should check the context

[bobbingwide]

I was developing a new plugin which handles its own display of a custom column.
During debugging, I registered the field using oik-types
When the column was being shown on a custom post type, bw_custom_column_admin() displayed the value using its own logic.
This was in addition to the custom column being formatted by the new plugin.
bw_custom_column_admin() should have checked that the column was a valid column for the given post type.

Workaround.

Remove the field registration

[bobbingwide]

Proposed solution

The code should determine the post type by querying the current filter, then look for the field name associated with the post type. bw_custom_column should only be called when it's a registered field.

bw_custom_column_admin() is in includes\bw_fields.inc so should be tested in tests\test-includes-bw-fields.php

The tests should be performed for both registered and unregistered fields.