left align partially hidden widget options

Upon opening a widget menu option, if that option is off the left-hand side of the screen it will now be left aligned (and visible).

This check only occurs when opening a widget option menu. If you were to open a menu and then resize the window, the menu's position will not be updated if the newly resized window forces the menu outside of the screen. @juliusv is this ok, or would you like to have an open menu checked when someone resizes the window?
nit: period ;)