Bug 9419: The highlight feature can cause a browser freeze

Bug 9419: The highlight feature can cause a browser freeze

Test plan:
- switch on the OpacHighlightedWords syspref
- search at the opac and intranet a string with a space (e.g.
  au,wrdl:"Shakespeare,  William" note the double space after the comma)
- without the patch your browser will be frozen during a few seconds,
  after applying it, the highlight works better.

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>
Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>