Reset crypto session pointers on RemoveKeys.

[ Merge of http://go/wvgerrit/189650 ]

The CDM session shares its CryptoSession instance with a few additional
member objects (CdmLicense and PolicyEngine).  When the CDM session's
crypto session is reset, it must also reset the CdmLicense and
PolicyEngine otherwise, a potential stale pointer reference may occur.

Test: request_license_test on Oriole
Test: WVTS on Oriole
Bug: 311239278
Change-Id: Ie175513ae652dcd96e12e5e1def574a8a56d5863

libwvdrmengine/cdm/core/src/policy_engine.cpp

@@ -39,9 +39,12 @@ PolicyEngine::PolicyEngine(CdmSessionId session_id,
     if (version >= kMinOemCryptoApiVersionSupportsRenewalDelayBase) {
       policy_timers_.reset(new PolicyTimersV18());
     }
+  } else {
+    LOGW("Failed to get API version: session_id = %s", IdToString(session_id));
   }
 
-  if (policy_timers_ == nullptr) {
+  if (!policy_timers_) {
+    // Use V16 policy timers if getting version failed.
     policy_timers_.reset(new PolicyTimersV16());
   }
   InitDevice(crypto_session);