discovery: properly exclude locally known but filtered heads
The conditional was a bit too narrow and produced buggy result when a node was
present in both common and heads (because it pleased the discovery) and it was
locally known but filtered.
This resulted in buggy getbundle request and server side crash.
basic test for hg debugrebuildstate
$ hg init repo
$ cd repo
$ touch foo bar
$ hg ci -Am 'add foo bar'
adding bar
adding foo
$ touch baz
$ hg add baz
$ hg rm bar
$ hg debugrebuildstate
state dump after
$ hg debugstate --nodates | sort
n 644 -1 set bar
n 644 -1 set foo
status
$ hg st -A
! bar
? baz
C foo
$ cd ..