[BUGFIX] Prevent registration of icons with empty path

The automatic registration of TCA record icons misses a check against
an empty source. This patch add this check and prevents registration
of icons without a path.

Resolves: #70159
Releases: master
Change-Id: Ibc507a369578c231afea7da516a6dfa061e00f17
Reviewed-on: http://review.typo3.org/43612


Reviewed-by: Stephan Großberndt <stephan@grossberndt.de>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>