Fix #1420400 - Fix several crashes with no open documents.
Fix #1420400 - Fix several crashes with no open documents.

PintaProject/Pinta,Fenex/Pinta,jakeclawson/Pinta,PintaProject/Pinta,Fenex/Pinta,PintaProject/Pinta,Mailaender/Pinta,Mailaender/Pinta,jakeclawson/Pinta