localrepo: move storevfs calculation out of if statement
In next patch, we will need this variable in else statement too. So, let's take
it out.
Differential Revision: https://phab.mercurial-scm.org/D9681
To run the tests, do:
cd tests/
python run-tests.py
See https://mercurial-scm.org/wiki/WritingTests for
more information on writing tests.