[PackageUsage] fix NPE

This is called by `mPm.getPackageUsage().maybeWriteAsync(mPm.mSettings.getPackagesLocked())` under `mPm.mLock` so it's unclear why any pkgSetting would be null. Perhaps there are other usages not shown in the stack  trace. Adding null pointer checks to avoid crashes.

BUG: 229823551
Test: builds
Change-Id: Ia33bb59824e774b02249a1e9872bc6e418dec658

services/core/java/com/android/server/pm/PackageUsage.java

@@ -66,7 +66,8 @@ class PackageUsage extends AbstractStatsBase<Map<String, PackageSetting>> {
             out.write(sb.toString().getBytes(StandardCharsets.US_ASCII));
 
             for (PackageSetting pkgSetting : pkgSettings.values()) {
-                if (pkgSetting.getPkgState().getLatestPackageUseTimeInMills() == 0L) {
+                if (pkgSetting == null || pkgSetting.getPkgState() == null
+                        || pkgSetting.getPkgState().getLatestPackageUseTimeInMills() == 0L) {
                     continue;
                 }
                 sb.setLength(0);