[ActivityManager] Avoid NullPointerException if no

crash info

Symptom:
This issue happens because the ANR process got killed
(because it crashed) before the ANR dialog dismissed.
In that case, the process record is marked as crashed
(ProcessRecord.crashing = true). When the ANR dialog
dismissed by user, it will cause NullPointerException
when writeToParcel while performing IPC because there
is no crash info (ApplicationErrorReport.crashInfo = null)

Solution:
Check crashinfo before access it

Change-Id: I2995de57684c1e13aab8297f5eea1e82ca3b7ad8