[core,rdp] Add a check for broken RDP security

RDP security is rarely used nowadays, but there have been reports about
situations where the encryption key is missing.
Add this check to properly terminate the connection in case of such an
unexpected event.

libfreerdp/core/security.c

@@ -730,6 +730,12 @@ BOOL security_encrypt(BYTE* data, size_t length, rdpRdp* rdp)
 {
 	BOOL rc = FALSE;
 	EnterCriticalSection(&rdp->critical);
+	if (!rdp->rc4_encrypt_key)
+	{
+		WLog_ERR(TAG, "[%s] rdp->rc4_encrypt_key=%p", __FUNCTION__, rdp->rc4_encrypt_key);
+		goto fail;
+	}
+
 	if (rdp->encrypt_use_count >= 4096)
 	{
 		if (!security_key_update(rdp->encrypt_key, rdp->encrypt_update_key, rdp->rc4_key_len, rdp))
@@ -763,8 +769,11 @@ BOOL security_decrypt(BYTE* data, size_t length, rdpRdp* rdp)
 	WINPR_ASSERT(rdp);
 
 	EnterCriticalSection(&rdp->critical);
-	if (rdp->rc4_decrypt_key == NULL)
+	if (!rdp->rc4_decrypt_key)
+	{
+		WLog_ERR(TAG, "[%s] rdp->rc4_decrypt_key=%p", __FUNCTION__, rdp->rc4_decrypt_key);
 		goto fail;
+	}
 
 	if (rdp->decrypt_use_count >= 4096)
 	{