fix(api): nvim_get_option_value does not clean up on FileType error #31219

Problem:
If there's an error in `FileType` autocmd, the filetype get-opt buffer
doesn't get cleaned up.

Solution:
Call `aucmd_restbuf`.

test/functional/lua/filetype_spec.lua

@@ -161,6 +161,18 @@ describe('vim.filetype', function()
       end
     end
   end)
+
+  it('.get_option() cleans up buffer on error', function()
+    api.nvim_create_autocmd('FileType', { pattern = 'foo', command = 'lua error()' })
+
+    local buf = api.nvim_get_current_buf()
+
+    exec_lua(function()
+      pcall(vim.filetype.get_option, 'foo', 'lisp')
+    end)
+
+    eq(buf, api.nvim_get_current_buf())
+  end)
 end)
 
 describe('filetype.lua', function()