Privacy: When path not created wp_mkdir_p() returns false, not WP_Error

[birgire]

In wp_privacy_generate_personal_data_export_file(), we have:

$result = wp_mkdir_p( $exports_dir );
if ( is_wp_error( $result ) ) {
	wp_send_json_error( $result->get_error_message() );
}

but the output of wp_mkdir_p() is only boolean.

[birgire]

44158.diff​ adjust the case when wp_mkdir_p() is unable to create the export folder.

[SergeyBiryukov]

In 43299:

Privacy: Correct the error check when creating an export folder in wp_privacy_generate_personal_data_export_file().

wp_mkdir_p() returns false on error, not a WP_Error object.

Props birgire.
Fixes #44158.

[SergeyBiryukov]

In 43300:

Privacy: Correct the error check when creating an export folder in wp_privacy_generate_personal_data_export_file().

wp_mkdir_p() returns false on error, not a WP_Error object.

Props birgire.
Merges [43299] to the 4.9 branch.
Fixes #44158.

[iandunn]

#44170 was marked as a duplicate.

[desrosj]

Moving all tickets in 4.9.7 to 4.9.8.

[SergeyBiryukov]

Moving already backported tickets back to 4.9.7.

[birgire]

#44205 was marked as a duplicate.