Don't segfault in ast_dot on NULL ast
Don't segfault in ast_dot on NULL ast

lutter/augeas,domcleal/augeas,kumy/augeas,kumy/augeas,hercules-team/augeas-do-not-use,dafugg/augeas,hercules-team/augeas,kunkku/augeas,bkearney/augeas,mchf/augeas,jjlin/augeas,raphink/augeas,camptocamp/augeas,hercules-team/augeas,dafugg/augeas,jtopjian/augeas,hercules-team/augeas-do-not-use,manandbytes/augeas,manandbytes/augeas,raphink/augeas,jasperla/augeas,kunkku/augeas,bkearney/augeas,pevalme/augeas,kumy/augeas,lutter/augeas,MikaelSmith/augeas,ptoscano/augeas,jasperla/augeas,pevalme/augeas,pevalme/augeas,kunkku/augeas,kumy/augeas,jjlin/augeas,mlichvar/augeas,domcleal/augeas,bkearney/augeas,mlichvar/augeas,GeoffWilliams/augeas,hercules-team/augeas-do-not-use,lutter/augeas,MikaelSmith/augeas,camptocamp/augeas,jjlin/augeas,camptocamp/augeas,jtopjian/augeas,bkearney/augeas,mlichvar/augeas,mchf/augeas,GeoffWilliams/augeas,ptoscano/augeas,camptocamp/augeas,ptoscano/augeas,domcleal/augeas,dafugg/augeas