fixed: KETCHER-472 (The Undo button should be enabled while there is a history of actions)
fixed: KETCHER-472 (The Undo button should be enabled while there is a history of actions)

ggasoftware/ketcher,ggasoftware/ketcher,ggasoftware/ketcher,ggasoftware/ketcher,ggasoftware/ketcher,ggasoftware/ketcher