[BUGFIX] file_get_contents default context

Check for default stream context.

Resolves: #70374
Releases: master
Change-Id: I88a3f49fa121e713707d54d7696ba1233a475220
Reviewed-on: http://review.typo3.org/43810


Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Reviewed-by: Ronald Klomp <rklomp@zigwebsoftware.nl>
Tested-by: Ronald Klomp <rklomp@zigwebsoftware.nl>
Reviewed-by: Eva Wiggers <eva_wiggers@hotmail.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>