hcrypto WinCNG backend: don't leak handles on crypto reinit

Similar fix to a88d0066, but for the WinCNG EVP backend. However this
is just a fix for leaking handles if the same EVP context is used with
a new key; there is no functionality issue as cipherstate is maintained
directly in the EVP context, not internally by WinCNG.

lib/hcrypto/evp-wincng.c

@@ -196,6 +196,11 @@ wincng_key_init(EVP_CIPHER_CTX *ctx,
     if (ctx->cipher->app_data == NULL)
 	return 0;
 
+    if (cng->hKey) {
+	BCryptDestroyKey(cng->hKey); /* allow reinitialization */
+	cng->hKey = (BCRYPT_KEY_HANDLE)0;
+    }
+
     /*
      * Note: ctx->key_len not EVP_CIPHER_CTX_key_length() for
      * variable length key support.