Fix nativeProcs being null.

dumpStackTraces originally checked this. This only happens when a silent
ANR is triggerred on a process name not in NATIVE_STACKS_OF_INTEREST.

Bug: 36414311
Bug: 36652737
Test: manual
Change-Id: I24402fb2ef2e08482f866dc1086ce83c1365d7ec
(cherry picked from commit 94a0dcdde12192ad0815ec88f8ac62152f6a58b4)
diff --git a/services/core/java/com/android/server/am/AppErrors.java b/services/core/java/com/android/server/am/AppErrors.java
index 7b1af38..c10f77c 100644
--- a/services/core/java/com/android/server/am/AppErrors.java
+++ b/services/core/java/com/android/server/am/AppErrors.java
@@ -870,7 +870,7 @@
             nativeProcs = NATIVE_STACKS_OF_INTEREST;
         }
 
-        int[] pids = Process.getPidsForCommands(nativeProcs);
+        int[] pids = nativeProcs == null ? null : Process.getPidsForCommands(nativeProcs);
         ArrayList<Integer> nativePids = null;
 
         if (pids != null) {