repoview: avoid wrapping changelog if there's nothing to filter
This simplifies the code a bit by moving the optimizaton for no
filtered revisions to one place. I assume it also makes working with
repos without obsmarkers a little faster, but it doesn't seem
significant.
Differential Revision: https://phab.mercurial-scm.org/D7248
$ hg init
$ echo a > a
$ hg ci -Am t
adding a
$ hg mv a b
$ hg ci -Am t1
$ hg debugrename b
b renamed from a:b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3
$ hg mv b a
$ hg ci -Am t2
$ hg debugrename a
a renamed from b:37d9b5d994eab34eda9c16b195ace52c7b129980
$ hg debugrename --rev 1 b
b renamed from a:b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3