fix crash in flatten_thistype
fix crash in flatten_thistype

cquinn/ponyc,darach/ponyc,Theodus/ponyc,jemc/ponyc,mkfifo/ponyc,jemc/ponyc,boemmels/ponyc,CausalityLtd/ponyc,malthe/ponyc,Theodus/ponyc,jupvfranco/ponyc,mkfifo/ponyc,sgebbie/ponyc,Theodus/ponyc,shlomif/ponyc,Perelandric/ponyc,boemmels/ponyc,darach/ponyc,malthe/ponyc,ryanai3/ponyc,kulibali/ponyc,mkfifo/ponyc,Praetonus/ponyc,shlomif/ponyc,dipinhora/ponyc,Perelandric/ponyc,jemc/ponyc,doublec/ponyc,malthe/ponyc,Praetonus/ponyc,ponylang/ponyc,jupvfranco/ponyc,lukecheeseman/ponyta,Perelandric/ponyc,lukecheeseman/ponyta,jupvfranco/ponyc,doublec/ponyc,mkfifo/ponyc,darach/ponyc,influx6/ponyc,pap/ponyc,boemmels/ponyc,cquinn/ponyc,sgebbie/ponyc,pap/ponyc,CausalityLtd/ponyc,Theodus/ponyc,ponylang/ponyc,jonas-l/ponyc,Perelandric/ponyc,mkfifo/ponyc,dipinhora/ponyc,sgebbie/ponyc,gwelr/ponyc,cquinn/ponyc,jonas-l/ponyc,boemmels/ponyc,ryanai3/ponyc,kulibali/ponyc,sgebbie/ponyc,influx6/ponyc,ponylang/ponyc,CausalityLtd/ponyc,Theodus/ponyc,malthe/ponyc,kulibali/ponyc,Praetonus/ponyc,ryanai3/ponyc,jonas-l/ponyc,jupvfranco/ponyc,kulibali/ponyc,Praetonus/ponyc,Perelandric/ponyc,jupvfranco/ponyc,dckc/ponyc,dipinhora/ponyc,cquinn/ponyc,gwelr/ponyc,sgebbie/ponyc,boemmels/ponyc,doublec/ponyc,lukecheeseman/ponyta,pap/ponyc,dckc/ponyc