CRM-14224 - CRM_Upgrade_Incremental_php_FourFour - Fix isValidWordReplacement()

The conditional was incorrect -- most likely an incomplete refactoring from
(eg isInvalid => isValid).
Merge pull request #3538 from totten/4.4-wordrep

CRM-14224 - CRM_Upgrade_Incremental_php_FourFour - Fix isValidWordReplacement()