Avoid class not found error for CRM_Contact_Form_Search_Custom_Base when upgrading to 5.43

See dev/core#2923 (closed)

Similar to !92 (merged), but now in 5.43 the temporary patch in core is no longer there so you get same the error about CRM_Contact_Form_Search_Custom_Base but from this other spot in hook_container.

mentioned in issue dev/core#2923 (closed)

I have tested this patch and the upgrades from versions < 5.41 are now successful and I have not seen any issues on the existing data processors.

Thanks for all your testing on this issue.

mentioned in commit b66b986b

merged

Thanks @DaveD for the patch and thanks @kcristiano for testing

mentioned in commit 5bf4b984