factor out regexp so it is not defined multiple times
when adding _x_org_koala-framework_last extension check for valid line numbers

this is required to be able to correctly concat files
_x_org_koala-framework_last is always an object (as it is when parsed using json_decode
implement concat offset correction a bit different

don't add an additional block, chrome somehow doesn't like that.

instead correct the offset for the first found block