[ActivityManager] Avoid system server crash due to package removed

Symptom:
When application is not responding, an ANR dialog will shown.
In certain timing, user uninstall the application when the ANR
occurs, but before ANR dialog shown. The system server will crash
when looking up the errorReportReceiver because the package is removed.

Here shows how the exception occurs.
java.lang.IllegalArgumentException: Unknown package: app.package.name
 at com.android.server.pm.Settings.getInstallerPackageNameLPr
 at com.android.server.pm.PackageManagerService.getInstallerPackageName
 at android.app.ApplicationPackageManager.getInstallerPackageName
 at android.app.ApplicationErrorReport.getErrorReportReceiver
 at com.android.server.am.ActivityManagerService.startAppProblemLocked
 at com.android.server.am.ActivityManagerService.makeAppNotRespondingLocked
 at com.android.server.am.ActivityManagerService.appNotResponding

Change-Id: Iced4287bd44dc25b1db2c1e3a583892eb6c041a2