Fixed intermittent failure in GTS test.

Need to clear mEncKey in constructor, otherwise, decrypted data is wrong.

bug: 15540382
Change-Id: I0e2d4d6edd8a5800fa2a36e9f258782edc493e13

proprietary/cryptoPlugin/WVCryptoPlugin.cpp

@@ -46,6 +46,8 @@ const uint8_t WVCryptoFactory::kUUIDWidevine[16] = {
 WVCryptoPlugin::WVCryptoPlugin(const void *data, size_t size)
     : mInitCheck(NO_INIT)
 {
+    memset(mEncKey, 0, sizeof(mEncKey));
+
     // not using data at this time, require
     // size to be zero.
     if (size > 0) {