Remove redundant _context checks during ThreadWorker creation
Remove redundant _context checks during ThreadWorker creation

- `RunInner` is private and can only be run from `Run`
- `Run` is private and is only every invoked from the constructor
- _context has no default value at construction so must be null during
  `Run` & `RunInner`

eksperts/fuselibs-public,eksperts/fuselibs-public,kusma/fuselibs-public,yupferris/fuselibs-public,nekronos/fuselibs-public,cbaggers/fuselibs-public,nekronos/fuselibs-public,kusma/fuselibs-public,fusetools/fuselibs-public,yupferris/fuselibs-public,nekronos/fuselibs-public,nekronos/fuselibs-public,fusetools/fuselibs-public,eksperts/fuselibs-public,kusma/fuselibs-public,yupferris/fuselibs-public,eksperts/fuselibs-public,nekronos/fuselibs-public,fusetools/fuselibs-public,fusetools/fuselibs-public,eksperts/fuselibs-public,kusma/fuselibs-public,cbaggers/fuselibs-public,nekronos/fuselibs-public,yupferris/fuselibs-public,kusma/fuselibs-public,cbaggers/fuselibs-public,yupferris/fuselibs-public,fusetools/fuselibs-public,nekronos/fuselibs-public,yupferris/fuselibs-public,kusma/fuselibs-public,fusetools/fuselibs-public,eksperts/fuselibs-public,cbaggers/fuselibs-public,kusma/fuselibs-public,fusetools/fuselibs-public,cbaggers/fuselibs-public,eksperts/fuselibs-public,yupferris/fuselibs-public,cbaggers/fuselibs-public,cbaggers/fuselibs-public