[fixed] Tweak setting change - crash

[Geta-Ve]

Nope, not fixed. (as an aside, I like how the crashes are handled now)

Dump:

Dump written 2015-9-14_20-3
Version: 2.0.1
Window: geom
Reason: {badmatch,{0.25098039215686274,0.5882352941176471,1.0}}

Short stack trace:
[]

Long stack trace:
[{wings_tweak,'-draw_magnet/1-fun-0-',3,
[{file,"wings_tweak.erl"},{line,1460}]},
{lists,foldl,3,[{file,"lists.erl"},{line,1262}]},
{wings_tweak,handle_magnet_event,2,[{file,"wings_tweak.erl"},{line,552}]},
{wings_wm,handle_event,3,[{file,"wings_wm.erl"},{line,931}]},
{wings_wm,send_event,2,[{file,"wings_wm.erl"},{line,903}]},
{wings_wm,do_dispatch,2,[{file,"wings_wm.erl"},{line,767}]},
{lists,foreach,2,[{file,"lists.erl"},{line,1337}]},
{wx,foreach,2,[{file,"wx.erl"},{line,193}]}]