Fix `lorri direnv` triggering an unconditional rebuild every time it is run.
After fixing up the build loop people suddenly started noticing that
lorri was evaluating every time something ran `lorri direnv`, which
could potentially be every time the user switched between buffers in
the editor.
This is not the intended behaviour, since we should run an
unconditional build only the first time the project is added to the
watcher, and after rely on the watcher to notify us of any file
changes (or the user running `lorri internal ping` to force a
rebuild).
dfafbdd56c