fix: recover toggle_checkbox util's condition to create a checkbox wi…

…th a line without a checkbox

lua/obsidian/util.lua

@@ -506,7 +506,7 @@ util.toggle_checkbox = function(opts)
     if string.match(line, unordered_list_pattern) then
       line = string.gsub(line, unordered_list_pattern, "%1- [ ] %2")
     else
-      return
+      line = string.gsub(line, "^(%s*)", "%1- [ ] ")
     end
   else
     for i, check_char in enumerate(checkboxes) do