Corrections to widevine plugin for vts tests

Add a check for invalid session size in restoreKeys
and correct the return code when attempting to create a
plugin with an invalid uuid. Also correct the return code
when attempting to decrypt after keys have been removed.

bug:37172151
Change-Id: I7e832ffe04081471a0cdb3a9329808f47f12cfc3

libwvdrmengine/mediadrm/src/WVDrmPlugin.cpp

@@ -314,6 +314,9 @@ status_t WVDrmPlugin::removeKeys(const Vector<uint8_t>& sessionId) {
 
 status_t WVDrmPlugin::restoreKeys(const Vector<uint8_t>& sessionId,
                                   const Vector<uint8_t>& keySetId) {
+  if (sessionId.size() == 0 || keySetId.size() == 0) {
+    return android::BAD_VALUE;
+  }
   CdmSessionId cdmSessionId(sessionId.begin(), sessionId.end());
   CdmKeySetId cdmKeySetId(keySetId.begin(), keySetId.end());