WP_List_Table::single_row_columns() needs to do an exact comparison

[Viper007Bond]

If for whatever reason you pass a column ID of 0 when dealing with a list table, WordPress thinks it's a checkbox column because of the loose comparison, i.e. == instead of ===.

Since I don't see why passing a number instead of a string shouldn'r be allowed, attached is a patch.

[scribu]

Are you saying 'cb' == 0 evals to true?

[scribu]

D'oh. Yes, it does. Seems PHP's type coercion is at least as treacherous as the one in JavaScript.

[kurtpayne]

I can reproduce the original bug. The patch looks good.

[nacin]

Would if ( 'cb' == $column_key ) in print_column_headers() also be affected?

[Viper007Bond]

Seems like it would be affected, yes.

I can't test though because I don't remember exactly what I was working on at the time other than maybe I was creating columns programically using a numeric array.

[nacin]

I'm going to go with a column ID of "0" being invalid and punt this until we are able to fix it everywhere.

[wonderboymusic]

In 34383:

List Tables: when comparing string literals (non-numeric in nature) against vars, strict comparison can/should be used.

Props wonderboymusic, Viper007Bond.
Fixes #21249.