Only load the config file into the default libctx if necessary

Only load the config file into the default libctx if necessary

There is no need to load providers from the config file into the default
libctx, if the current libctx that we are using isn't the default libctx.
This avoids some deadlock situations.

Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/14991)