bitbake: runqueue.py: Fix a virtual class extension stamps issue

The file_name parameter passed to bb.parse.siggen.invalidate_task
should be a virtual file name instead of a real file name, or else you
will encounter a following error, for instance, when you run:

$ bitbake nativesdk-lzip -c unpack -f

the error arise:
| ERROR: An uncaught exception occurred in runqueue
| if file_name:
|    > taintfn = d.stamp[file_name] + '.' + task + '.taint'
| else:
| KeyError: 'virtual:nativesdk:/opt/poky/meta/recipes-extended/lzip/lzip_1.19.bb'

when multilib builds are used on OE.

(Bitbake rev: da37bdad46e11e7ce93ba7a59d58757b769dc16b)

Signed-off-by: Ming Liu <liu.ming50@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/runqueue.py

@@ -1093,7 +1093,7 @@ class RunQueueData:
                     bb.debug(1, "Task %s is marked nostamp, cannot invalidate this task" % taskname)
             else:
                 logger.verbose("Invalidate task %s, %s", taskname, fn)
-                bb.parse.siggen.invalidate_task(taskname, self.dataCaches[mc], fn)
+                bb.parse.siggen.invalidate_task(taskname, self.dataCaches[mc], taskfn)
 
         self.init_progress_reporter.next_stage()