bitbake: bitbake-worker: Fix bitbake -n

Without this you see:

File "bitbake/bin/bitbake-worker", line 201, in fork_off_task
    os._exit(child())
TypeError: an integer is required

(Bitbake rev: cd477b5e77ab0373248b8a8fa30e1c7b8ea984fd)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/bin/bitbake-worker

@@ -193,8 +193,9 @@ def fork_off_task(cfg, data, workerdata, fn, task, taskname, appends, taskdepdat
                     logger.critical(str(exc))
                 os._exit(1)
             try:
-                if not cfg.dry_run:
-                    return bb.build.exec_task(fn, taskname, the_data, cfg.profile)
+                if cfg.dry_run:
+                    return 0
+                return bb.build.exec_task(fn, taskname, the_data, cfg.profile)
             except:
                 os._exit(1)
         if not profiling: