Unable to update equipment_models which have no checkin/out procedures

[dgoerger]

Commit 78ef7bf for #470 needs a check to ensure we're not calling phase_params.each on an empty phase_params.

def delete_procedures(params, phase)
      # phase needs to be equal to either "checkout" or "checkin"
      phase_params = params[:equipment_model][:"#{phase}_procedures_attributes"]
      phase_params.each do |k, v|

Currently on Development, updating an equipment model which does not have any checkin or checkout procedures fails (EDIT: either no checkin procedures OR no checkout procedures, or none of either), on account of cannot call .each on NIL.

This is a pretty severe bug; it should frankly be backported to 3.2.x, but it's also probably it won't affect most of our clients, given the improbability of having equipment with no in/out procedures. But still.