Use unsigned calling_uid in case of bug report triggered from adb

The utility method to extract user_id and app_id from calling_uid
takes unsigned int_32. Changed the default value of calling_uid to
0 from -1 for the case when bug report is triggered by adb and calling_uid is not relevant.

Bug: 260989962
Test: tested manually by initiating a bug report through adb and
observing the BUGREPORT_STARTED broadcast in logcat.
Ignore-AOSP-First: will do it later with other headless changes.

Change-Id: I1c410853ef99c6292039382714394066a72318f7