lib: Make callers of base64_encode_data_blob check for success

lib: Make callers of base64_encode_data_blob check for success

Quite a few callers already did check for !=NULL. With the current code this is
pointless due to a SMB_ASSERT in base64_encode_data_blob() itself. Make the
callers consistently check, so that we can remove SMB_ASSERT from base64.c.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>