Fix for CamelCase filter when string contains multiple uppercase letters and Unicode is off

`Zend\Filter\Word\CamelCaseToSeparator` fails with strings containing camel case, non-word chars and multiple uppercase letters. This only happens when PCRE was compiled without Unicode support.

 | TheseAre_SOME_CamelCASEDWords
-----|-----|-----
`StringUtils::hasPcreUnicodeSupport() == true` | These_Are_SOME_Camel_CASED_Words
`StringUtils::hasPcreUnicodeSupport() == false` | These_Are_SOM_E_Camel_CASED_Words

Unit test and fix attached to this PR.