Remove unnecessary null pointer checks
Merge pull request #136 from mpark/if_delete

Remove unnecessary null pointer checks
Generic lambdas aren't quite ready in g++-4.9.0.
Remove unnecessary assert

The code is properly guarded from not mucking with a shutting down job runner just a few lines below already.

Fixes #137
Merge pull request #139 from mpark/gdb-fix

Generic lambdas aren't quite ready in g++-4.9.0.
Merge pull request #140 from cmaloney/issue-137

Remove unnecessary assert