rs274: Guard NULL _setup.file_pointer
rs274: Guard NULL _setup.file_pointer

If reset is called from close where file_pointer is first nulled
code may fail.

Signed-off-by: Pavel Shramov <a3acfc595bcbd4448198c0a959d48defb367e4b1@mexmat.net>

EqAfrica/machinekit,ArcEye/MK-Qt5,unseenlaser/machinekit,ianmcmahon/linuxcnc-mirror,bmwiedemann/linuxcnc-mirror,unseenlaser/machinekit,RunningLight/machinekit,ArcEye/MK-Qt5,mhaberler/machinekit,jaguarcat79/ILC-with-LinuxCNC,narogon/linuxcnc,Cid427/machinekit,araisrobo/linuxcnc,araisrobo/linuxcnc,cnc-club/linuxcnc,araisrobo/linuxcnc,ArcEye/machinekit-testing,cdsteinkuehler/MachineKit,kinsamanka/machinekit,mhaberler/machinekit,kinsamanka/machinekit,unseenlaser/machinekit,EqAfrica/machinekit,strahlex/machinekit,araisrobo/machinekit,narogon/linuxcnc,Cid427/machinekit,bobvanderlinden/machinekit,EqAfrica/machinekit,RunningLight/machinekit,cdsteinkuehler/linuxcnc,ArcEye/MK-Qt5,Cid427/machinekit,mhaberler/machinekit,bobvanderlinden/machinekit,unseenlaser/machinekit,cdsteinkuehler/MachineKit,unseenlaser/machinekit,araisrobo/machinekit,Cid427/machinekit,RunningLight/machinekit,EqAfrica/machinekit,strahlex/machinekit,bobvanderlinden/machinekit,mhaberler/machinekit,ikcalB/linuxcnc-mirror,strahlex/machinekit,ikcalB/linuxcnc-mirror,cnc-club/linuxcnc,kinsamanka/machinekit,ArcEye/machinekit-testing,Cid427/machinekit,cnc-club/linuxcnc,unseenlaser/linuxcnc,cnc-club/linuxcnc,RunningLight/machinekit,araisrobo/machinekit,cdsteinkuehler/linuxcnc,Cid427/machinekit,araisrobo/machinekit,unseenlaser/linuxcnc,ArcEye/MK-Qt5,ArcEye/MK-Qt5,cdsteinkuehler/MachineKit,cnc-club/linuxcnc,jaguarcat79/ILC-with-LinuxCNC,RunningLight/machinekit,araisrobo/linuxcnc,ArcEye/machinekit-testing,bobvanderlinden/machinekit,ArcEye/machinekit-testing,EqAfrica/machinekit,aschiffler/linuxcnc,RunningLight/machinekit,bobvanderlinden/machinekit,ianmcmahon/linuxcnc-mirror,cdsteinkuehler/MachineKit,Cid427/machinekit,aschiffler/linuxcnc,bmwiedemann/linuxcnc-mirror,ArcEye/MK-Qt5,ianmcmahon/linuxcnc-mirror,ArcEye/machinekit-testing,EqAfrica/machinekit,strahlex/machinekit,unseenlaser/machinekit,EqAfrica/machinekit,ikcalB/linuxcnc-mirror,jaguarcat79/ILC-with-LinuxCNC,strahlex/machinekit,RunningLight/machinekit,araisrobo/machinekit,unseenlaser/machinekit,araisrobo/machinekit,aschiffler/linuxcnc,cnc-club/linuxcnc,cdsteinkuehler/linuxcnc,unseenlaser/machinekit,kinsamanka/machinekit,ikcalB/linuxcnc-mirror,cdsteinkuehler/MachineKit,ianmcmahon/linuxcnc-mirror,ianmcmahon/linuxcnc-mirror,ArcEye/MK-Qt5,unseenlaser/linuxcnc,mhaberler/machinekit,bmwiedemann/linuxcnc-mirror,kinsamanka/machinekit,kinsamanka/machinekit,ianmcmahon/linuxcnc-mirror,strahlex/machinekit,ianmcmahon/linuxcnc-mirror,kinsamanka/machinekit,aschiffler/linuxcnc,narogon/linuxcnc,narogon/linuxcnc,unseenlaser/linuxcnc,narogon/linuxcnc,strahlex/machinekit,EqAfrica/machinekit,kinsamanka/machinekit,RunningLight/machinekit,bobvanderlinden/machinekit,Cid427/machinekit,cdsteinkuehler/MachineKit,jaguarcat79/ILC-with-LinuxCNC,ikcalB/linuxcnc-mirror,ArcEye/machinekit-testing,mhaberler/machinekit,ArcEye/MK-Qt5,mhaberler/machinekit,unseenlaser/linuxcnc,cdsteinkuehler/linuxcnc,ArcEye/machinekit-testing,bobvanderlinden/machinekit,mhaberler/machinekit,cdsteinkuehler/linuxcnc,ikcalB/linuxcnc-mirror,bmwiedemann/linuxcnc-mirror,cnc-club/linuxcnc,ikcalB/linuxcnc-mirror,araisrobo/machinekit,araisrobo/machinekit,ArcEye/machinekit-testing,araisrobo/machinekit,bobvanderlinden/machinekit,cdsteinkuehler/linuxcnc,bmwiedemann/linuxcnc-mirror,jaguarcat79/ILC-with-LinuxCNC,bmwiedemann/linuxcnc-mirror,bmwiedemann/linuxcnc-mirror,aschiffler/linuxcnc,araisrobo/linuxcnc