Fix null-deref crash while fuzzing

When random parcel is sent to incidentd, AIDL service
crashes with null pointer dereference.

Test: atest incidentd_test
Test: m incidentd_service_fuzzer && adb sync data && adb shell /data/fuzz/x86_64/incidentd_service_fuzzer/incidentd_service_fuzzer
Bug: 282963041
Change-Id: I0e0ebc479acbfd3f5e9f56b629380b5d90021f45