Fix: Possible more async read writes to stylecache
Fix: Possible more async read writes to stylecache

- Hannes pointed out that there might be more async read writes to stylecache and hence the whole block is in a mutex
lock.

quitejonny/tangram-es,tangrams/tangram-es,tangrams/tangram-es,cleeus/tangram-es,cleeus/tangram-es,quitejonny/tangram-es,tangrams/tangram-es,xvilan/tangram-es,xvilan/tangram-es,xvilan/tangram-es,cleeus/tangram-es,quitejonny/tangram-es,cleeus/tangram-es,xvilan/tangram-es,cleeus/tangram-es,quitejonny/tangram-es,tangrams/tangram-es,tangrams/tangram-es,tangrams/tangram-es,cleeus/tangram-es,quitejonny/tangram-es,quitejonny/tangram-es,tangrams/tangram-es