Fix NPE for MATCH_FACTORY_ONLY

Bug: 28087606
Change-Id: Ib86c5189aa9a9ca87504625dd19bdeab56fd4967
diff --git a/services/core/java/com/android/server/pm/PackageManagerService.java b/services/core/java/com/android/server/pm/PackageManagerService.java
index fbf4c0c..cc4f31a 100644
--- a/services/core/java/com/android/server/pm/PackageManagerService.java
+++ b/services/core/java/com/android/server/pm/PackageManagerService.java
@@ -3036,7 +3036,7 @@
             }
             if (p == null) {
                 p = mPackages.get(packageName);
-                if (matchFactoryOnly && !isSystemApp(p)) {
+                if (matchFactoryOnly && p != null && !isSystemApp(p)) {
                     return null;
                 }
             }