Add missing null check on start of SipIncomingCallReceiver received.

Test: Ran ADB command to start receiver; verified no crash.
Fixes: 129903757
Merged-In: I5b7757f97a5c53643e20850a6d7aeb7074eb19d7
Change-Id: I5b7757f97a5c53643e20850a6d7aeb7074eb19d7
(cherry picked from commit 8e1e354b0f617b0a8373a94c935c0c6e39abd9ef)
1 file changed