openssl: Fix openssl engines

- Return CURLE_OK if the engine successfully loaded.

Prior to this change:

When loading an openssl engine, the result code is initialized to
CURLE_SSL_ENGINE_NOTFOUND, but is never set to CURLE_OK when the engine
was successfully loaded. This causes curl to error out, falsely stating
engine not found when it actually was.

Broken since f2ce6c46 (precedes 8.14.0) which added support for using
engines and providers at the same time.

Fixes https://github.com/curl/curl/issues/17617
Closes https://github.com/curl/curl/pull/17618

lib/vtls/openssl.c

@@ -1907,6 +1907,9 @@ static CURLcode ossl_set_engine(struct Curl_easy *data, const char *name)
       result = CURLE_SSL_ENGINE_INITFAILED;
       e = NULL;
     }
+    else {
+      result = CURLE_OK;
+    }
     data->state.engine = e;
     return result;
   }