flake.nixConfig: fix flake-registry config settings

Before this commit, nixConfig.flake-registry didn't have any real effect
on the evaluation, since config was applied after inputs were evaluated.
Change this behavior: apply the config in the beginning of flake::lockFile.

src/libcmd/installables.cc

@@ -575,8 +575,6 @@ std::shared_ptr<flake::LockedFlake> InstallableFlake::getLockedFlake() const
 {
     if (!_lockedFlake) {
         _lockedFlake = std::make_shared<flake::LockedFlake>(lockFlake(*state, flakeRef, lockFlags));
-        _lockedFlake->flake.config.apply();
-        // FIXME: send new config to the daemon.
     }
     return _lockedFlake;
 }

src/libexpr/flake/flake.cc

@@ -298,6 +298,9 @@ LockedFlake lockFlake(
 
     auto flake = getFlake(state, topRef, lockFlags.useRegistries, flakeCache);
 
+    flake.config.apply();
+    // FIXME: send new config to the daemon.
+
     try {
 
         // FIXME: symlink attack