fix: build & empty doc entries

Fixed build error and empty doc entries when the pattern is not found.

Author: luckasRanarison

lua/nvim-devdocs/operations.lua

@@ -203,6 +203,8 @@ M.filter_doc = function(lines, pattern)
     if found then table.insert(filtered_lines, line) end
   end
 
+  if not found then return lines end
+
   return filtered_lines
 end
 

lua/nvim-devdocs/transpiler.lua

@@ -277,7 +277,7 @@ function transpiler:eval(node)
       result = "\n```" .. attributes["data-language"] .. "\n" .. result .. "\n```\n"
     elseif tag_name == "pre" and attributes["class"] then
       local language = attributes["class"]:match("language%-(.+)")
-      result = "\n```" .. language .. "\n" .. result .. "\n```\n"
+      result = "\n```" .. (language or "") .. "\n" .. result .. "\n```\n"
     elseif tag_name == "abbr" then
       result = string.format("%s(%s)", result, attributes.title)
     elseif tag_name == "iframe" then