lazyplug: add mutex & boolean check for lazy mode

Multiple callers, instances can call lazyplug_enter_lazy().
Fix race-conditions via mutex & boolean.

Thanks to hsk from Matcl for debugging this.

Signed-off-by: Park Ju Hyung <qkrwngud825@gmail.com>

Original commit: https://github.com/halaszk/Perseus-halaszk-universal5433/commit/6dca5e2f8fd42ffb91baf545f1843a8a0e6c0fa3