[BUGFIX] Fallback to version of ext_emconf.php

To resolve dependencies the ExtensionManager needs a version of an
extension. If the current composer.json fails to provide a version
we should fall back to the ext_emconf.php.

Releases: master
Resolves: #65866
Change-Id: I9e8383de10e2df1b722fda4b55d1379908f13138
Reviewed-on: http://review.typo3.org/41133


Reviewed-by: Benjamin Mack <benni@typo3.org>
Tested-by: Benjamin Mack <benni@typo3.org>
Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Tested-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>