hgweb: handle None from templatedir() equally bad in webcommands.py
The following paragraph is based just on my reading of the code; I
have not tried to test it.
Before my recent work on templates in frozen binaries, it seems both
hgwebdir_mod.py and webcommands.py would pass in an empty list
into staticfile() when running in a frozen binary. That would then
result in a variable in that function (path) not getting bound
before its first use. I then changed that without thinking in D8786 so
we passed a None value into the function, which made it break in
another way (trying to iterate over None). Then I tried to fix it up
in D8810, but I only changed hgwebdir_mod.py for some reason, and it
still doesn't actually work in frozen binaries (which seems fair,
since was broken before my changes too).
This patch just replicates the half-assed "fix" from D8810 in
webcommands.py, so they look more similar so I can start refactoring
them in the same way.
Differential Revision: https://phab.mercurial-scm.org/D8933