Freezer: skip killed app

It's not necessary to unfreeze an already killed app.

Bug: 213395752
Test: No "Unable to query binder frozen info for pid 0" in logcat.
Change-Id: I87f182031363065fde570ae99d04ed5dc0b31e4c

services/core/java/com/android/server/am/CachedAppOptimizer.java

@@ -962,7 +962,7 @@ public final class CachedAppOptimizer {
         }
 
         opt.setFreezerOverride(false);
-        if (!opt.isFrozen()) {
+        if (pid == 0 || !opt.isFrozen()) {
             return;
         }