src: turn key length exception into CHECK

This exception can logically never happen because of the key stretching
that takes place first.  Failure must therefore be a bug in Node.js and
not in the executing script.

PR-URL: nodejs#15183
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: bnoordhuis

src/node_crypto.cc

@@ -3363,10 +3363,7 @@ void CipherBase::Init(const char* cipher_type,
   if (mode == EVP_CIPH_WRAP_MODE)
     EVP_CIPHER_CTX_set_flags(&ctx_, EVP_CIPHER_CTX_FLAG_WRAP_ALLOW);
 
-  if (!EVP_CIPHER_CTX_set_key_length(&ctx_, key_len)) {
-    EVP_CIPHER_CTX_cleanup(&ctx_);
-    return env()->ThrowError("Invalid key length");
-  }
+  CHECK_EQ(1, EVP_CIPHER_CTX_set_key_length(&ctx_, key_len));
 
   EVP_CipherInit_ex(&ctx_,
                     nullptr,