fix: add nil check on current line

Author: MeanderingProgrammer

lua/render-markdown/handler/markdown_inline.lua

@@ -74,7 +74,8 @@ function Handler:shortcut(info)
         return
     end
 
-    if info:line('on'):find('[' .. info.text .. ']', 1, true) ~= nil then
+    local line = info:line('on')
+    if line ~= nil and line:find('[' .. info.text .. ']', 1, true) ~= nil then
         self:wiki_link(info)
         return
     end

lua/render-markdown/node_info.lua

@@ -126,7 +126,7 @@ function NodeInfo:for_each_child(callback)
 end
 
 ---@param position 'above'|'below'|'on'
----@return string
+---@return string?
 function NodeInfo:line(position)
     local start_row = nil
     if position == 'above' then