arc: patterns do not save with collections

[dndrks]

current behavior: when saving a collection with an arc pattern, the white square next to save doesn't appear and my collection isn't saved
expected behavior: saving a collection with an arc pattern should save the arc pattern and the rest of the parameters
maiden output:

lua: 
/home/we/dust/code/cc-gm/cheat_codes.lua:4858: attempt to concatenate a nil value (field 'count')
stack traceback:
	/home/we/dust/code/cc-gm/cheat_codes.lua:4858: in global 'save_arc_pattern'
	/home/we/dust/code/cc-gm/cheat_codes.lua:3855: in field 'action'
	/home/we/norns/lua/core/params/trigger.lua:35: in function 'core/params/trigger.bang'
	/home/we/norns/lua/core/params/trigger.lua:23: in function 'core/params/trigger.set'
	(...tail calls...)
	/home/we/norns/lua/core/menu/params.lua:179: in function 'core/menu/params.key'
	/home/we/norns/lua/core/menu.lua:139: in function </home/we/norns/lua/core/menu.lua:116>

[dndrks]

fixed in #17