[BUGFIX] Scheduler now throws OutOfBoundsException on SQL query error

If the query for fetchTask fails for whatever reason, scheduler will
now gracefully throw an exception instead of assuming it had gotten
a valid resource pointer

Resolves: #67463
Related: #39085
Releases: master, 6.2
Change-Id: I26819df3fd173b36de6121100a6398ed4b701319
Reviewed-on: http://review.typo3.org/40256


Reviewed-by: Lienhart Woitok <lienhart.woitok@netlogix.de>
Tested-by: Lienhart Woitok <lienhart.woitok@netlogix.de>
Reviewed-by: Stephan Großberndt <stephan@grossberndt.de>
Reviewed-by: Benjamin Mack <benni@typo3.org>
Tested-by: Benjamin Mack <benni@typo3.org>