Prevent null result when no matches found

In some instances a null value is returned when there are no matches, even when the original string should be shown (e.g. http://www.concrete5.org/developers/bugs/5-6-1-2/file-manager-search-shows-no-title-if-keyword-is-in-attribute-ra/)
Merge branch 'patch-10' of github.com:melat0nin/concrete5 into merge_prevent_highlight_search_return_null
Return `$value` in `highlightSearch`

Return `$value` in `TextHelper::highlightSearch()`

- Remove else
Merge pull request #1164 from mkly/merge_prevent_highlight_search_return_null

Merge prevent highlight search return null