wp-db: Always adds a filter on every query

[withinboredom]

It appears that in the function placeholder_escape it adds a filter remove_placeholder_escape. It adds a filter with the priority of 0. However, has_filter doesn't return true or false, it returns the priority. Since the priority is 0, it always adds a filter on every call. This issue is minor because WP_Hook prevents the infinite loop that would occur, however, it still causes a small amount of memory to be used and causes a small performance penalty.

[withinboredom]

Previous patch was incorrect

[SergeyBiryukov]

Introduced in [42056].

[SergeyBiryukov]

In 45707:

Database: Use a strict comparison for has_filter() check in wpdb::placeholder_escape().

The filter is added with a priority of 0, so a loose comparison had an unintended effect of adding the filter on every call.

Props withinboredom.
Fixes #47430.

[SergeyBiryukov]

#48843 was marked as a duplicate.