Fix Shift+Click action being cancelled with no gui

[DNx5]

Add check to make sure the player's chronology is not empty.

[SnowyCoder]

Thanks for reporting but we are resolving the issue in another way (removing the entry from the map when the chronology is empty) P.S. sorry but we can't merge even the last commit because all the classes were moved in the upper-core package and SlimyGuis became only like a wrapper for commands and for loading external files