Fix spurious "Timeout waiting for provider"

There is a race that if two clients are acquiring the same
content provider at the same momment, the second one would
create a new ContentProviderRecord and then start a new process.

Bug: 148953992
Test: Manual
Change-Id: I3e95be32208a0869dc0b399da70f767abdd76fb4

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

@@ -7156,7 +7156,7 @@ public class ActivityManagerService extends IActivityManager.Stub
                     } finally {
                         Binder.restoreCallingIdentity(ident);
                     }
-                } else if (dyingProc == cpr.proc) {
+                } else if (dyingProc == cpr.proc && dyingProc != null) {
                     // The old stable connection's client should be killed during proc cleaning up,
                     // so do not re-use the old ContentProviderRecord, otherwise the new clients
                     // could get killed unexpectedly.