devMotorAsyn.c: Set encoder ratio to 1 if ERES is 0 to avoid dividing by 0

[kmpeters]

Set encoder ratio to 1 if ERES is 0 in devMotorAsyn.c to avoid dividing by 0.

Fixes #213

[kmpeters]

This is a trivial change that doesn't really need a review. I'm trying to get into the habit of keeping people in the loop as changes happen.

[tboegi]

Is there a good reason to have a workaround in one driver (asyn)
and not in the motorRecord.cc ?

Somewhere around here :
/* Call device support to initialize itself and the driver */
if (pdset->base.init_record)

[kmpeters]

There is a check for ERES=0 in the motor record already:

motor/motorApp/MotorSrc/motorRecord.cc

Lines 692 to 696 in 8166246

	if (pmr->eres == 0.0)
	{
	pmr->eres = pmr->mres;
	MARK(M_ERES);
	}

I'm not sure why this wasn't sufficient protection in the case of the Gailil controller.

[MarkRivers]

I think the problem is that the encoder ratio is set in devMotorAsyn::init_controller

motor/motorApp/MotorSrc/devMotorAsyn.c

Line 185 in 8166246

eratio = pmr->mres / pmr->eres;

, which is called from devMotorAsyn::init_record

motor/motorApp/MotorSrc/devMotorAsyn.c

Line 418 in 8166246

init_controller(pmr, pasynUser);

. But in the motor_record.cc the device support init_record is called

motor/motorApp/MotorSrc/motorRecord.cc

Line 647 in 8166246

status = (*pdset->base.init_record) (pmr);

before the check for ERES=0

motor/motorApp/MotorSrc/motorRecord.cc

Line 692 in 8166246

if (pmr->eres == 0.0)