bridge: Add start_helper_process() assertion for valid argv
bridge: Add start_helper_process() assertion for valid argv

All the argvs here are completely under our control, but let's make sure
we don't screw up.

martinpitt/cockpit,cockpit-project/cockpit,martinpitt/cockpit,martinpitt/cockpit,mvollmer/cockpit,cockpit-project/cockpit,mvollmer/cockpit,mvollmer/cockpit,martinpitt/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,martinpitt/cockpit,mvollmer/cockpit,mvollmer/cockpit,cockpit-project/cockpit