[TASK] Avoid unused xpath when parsing locallang.xml

Increased performance by avoiding an xpath query if the requested
element is not 'target'.

Releases: master, 7.6
Resolves: #80016
Change-Id: I509de5bfb79701efe966d16bc29aaae6a46050ef
Reviewed-on: https://review.typo3.org/51851


Reviewed-by: Faton Haliti <fha@systime.dk>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Xavier Perseguers <xavier@typo3.org>
Tested-by: Xavier Perseguers <xavier@typo3.org>
Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>