fix: check for opts tbl in is_excluded_ft

• problem: attempt to index a nil value err
      solution: check for opts table before attempting to check if
                opts table contains anything else

      Should be considered a temporary fix. Validating the incoming
      options table should be its own functionality

lua/tidy/init.lua

@@ -1,7 +1,7 @@
 local M = {}
 
 local function is_excluded_ft(opts)
-    if not opts.filetype_exclude then
+    if not opts or not opts.filetype_exclude then
         return false
     end