Update ffxiv_skillmgr.lua

fixes gathering with skills in beta

applied this after aces recent commit 

fixes this error in beta 
failed with [string "C:\Minion\LuaMods\/minionlib/ml_utility.lua"]:118: attempt to index local 's'(a nil value)

also fixes another error when TimeSince is casted a nil value from skill.lastcast

ran all day using skills with gathering found no issues and skills work fine all code changes were commented except where added skillprofile variables
so happy reviewing