No error if asynPort not found

[anjohnson]

Segfaults later on if you try to connect to a port that doesn't exist.

## Connect Asyn port to simulator
drvAsynIPPortConfigure "VacSimPort", "localhost:9999", 0, 0, 0
st.cmd line 16: Command drvAsynIPPortConfigure not found.
createDnAsynSimulatedPLC "VacSimPLC", 1, "VacSimPort"
...
iocInit
Starting iocInit
############################################################################
## EPICS R7.0.2-C2-3
## EPICS Base built May  1 2019
############################################################################
devXiDnAsyn: Init mbbi called for "sioc2vac-sim:mode"
devXiDnAsyn: init_input invoked for "sioc2vac-sim:mode"
initDnAsynClient: Can't connect to Asyn port "VacSimPort":
	asynManager:connectDevice port VacSimPort not found 
devXiDnAsyn: Init bi called for "sioc2vac-sim:SP11"
devXiDnAsyn: init_input invoked for "sioc2vac-sim:SP11"
initDnAsynClient: Can't connect to Asyn port "VacSimPort":
	asynManager:connectDevice port VacSimPort not found 
...
devXiDnAsyn: Init ai called for "sioc2vac-sim:V7777"
devXiDnAsyn: init_input invoked for "sioc2vac-sim:V7777"
initDnAsynClient: Can't connect to Asyn port "VacSimPort":
	asynManager:connectDevice port VacSimPort not found 
Segmentation fault