Incoming call: Fix crash "Application tried to present a nil modal view controller on target <UISplitViewController: 0x13f833800>"
Incoming call: Fix crash "Application tried to present a nil modal view controller on target <UISplitViewController: 0x13f833800>"

Add some sanity checks

vector-im/riot-ios,vector-im/vector-ios,vector-im/riot-ios,vector-im/riot-ios,vector-im/riot-ios,vector-im/vector-ios,vector-im/vector-ios,vector-im/riot-ios,vector-im/riot-ios