Fix an RuntimeExcpetion in GsmDCT.onDataSetupComplete

Instead of throwing an exception when the connection between
the DCT and a DC is broken (i.e. its null) it is treated as
an error with a new cause. And thus will be handled as other
typical errors.

Bug: 5798643
Change-Id: I46f1660ae78f118b54ab62504809723ca302b2ef