custom_caret crashes settings textbox

[ergoithz]

Plugins: custom_caret, settings and lineguide used to reproduce the issue.

Clicking lineguide ruler "Add" dialog textbox will crash lite-xl if custom_caret is active (see screenshot), disabling custom_caret prevents the issue.

Error: /usr/share/lite-xl/core/doc/init.lua:287: attempt to compare number with nil

stack traceback:
	/usr/share/lite-xl/core/doc/init.lua:287: in function 'core.doc.sanitize_position'
	/usr/share/lite-xl/core/doc/init.lua:352: in function 'core.doc.get_char'
	/home/orpheus/.config/lite-xl/plugins/custom_caret.lua:115: in function 'core.docview.draw_caret'
	/usr/share/lite-xl/core/docview.lua:557: in upvalue 'draw_overlay'
	/usr/share/lite-xl/plugins/lineguide.lua:108: in function 'core.docview.draw_overlay'
	/home/orpheus/.config/lite-xl/libraries/widget/textbox.lua:98: in method 'draw'
	/home/orpheus/.config/lite-xl/libraries/widget/textbox.lua:298: in function 'libraries.widget.textbox.draw'
	/home/orpheus/.config/lite-xl/libraries/widget/init.lua:1268: in function 'libraries.widget.draw'
	/home/orpheus/.config/lite-xl/libraries/widget/dialog.lua:152: in function 'libraries.widget.dialog.draw'
	/usr/share/lite-xl/core/rootview.lua:483: in upvalue 'root_view_draw'
	/home/orpheus/.config/lite-xl/libraries/widget/init.lua:1468: in upvalue 'root_view_draw'
	...s/.config/lite-xl/plugins/plugin_manager/plugin_view.lua:66: in upvalue 'draw'
	/usr/share/lite-xl/plugins/autocomplete.lua:598: in upvalue 'root_view_draw'
	/usr/share/lite-xl/plugins/contextmenu.lua:32: in upvalue 'root_view_draw'
	/home/orpheus/.config/lite-xl/plugins/lsp/listbox.lua:520: in upvalue 'root_view_draw'
	/usr/share/lite-xl/plugins/treeview.lua:498: in function 'core.rootview.draw'
	/usr/share/lite-xl/core/init.lua:1341: in function 'core.step'
	/usr/share/lite-xl/core/init.lua:1401: in upvalue 'core_run'
	/home/orpheus/.config/lite-xl/plugins/settings.lua:1896: in function 'core.run'
	(...tail calls...)
	[string "local core..."]:14: in function <[string "local core..."]:6>
	[C]: in function 'xpcall'
	[string "local core..."]:6: in main chunk

[Guldoman]

Can repro.
The issue is that custom_caret expects that for each :update call there is up to 1 :draw call, which is a fair assumption.
But somewhere in widget (used by settings) :draw is getting called twice.