Added check to avoid debounce altogether if unnecessary

[lossanarch]

Even when setting -d 0 the command execution is still debounced enough that filesystem move events do not fire commands correctly (on MacOS 10.13.3) - a move will register an unlink and an add, but only fires the command for the add:
With -c echo {path} {event}:
mv test test1

unlink:test
add:test1
test1 add

This PR fixes the problem by checking if debounce is required at all (based on a non-zero debounce time) and if not required, launches the command with only throttling. This results in what I assume is the correct behaviour:
With -c echo {path} {event}:
mv test test1

unlink:test
add:test1
test unlink
test1 add

I hope this is helpful and many thanks for this project.

[XhmikosR]

Can you rebase this?

[sbleon]

I think this is effectively resolved in #90, which has been merged. This PR can probably be closed.