gkrellm crashes with transparent themes (e.g. invisible)

[Thomas Templin]

release: focal fossa
Version: gkrellm 2.3.10-2build2

Since focal fossa after start gkrellm crashes immideately if using a transparent theme:

(gkrellm:38820): GLib-CRITICAL **: 13:30:29.386: g_strstr_len: assertion 'haystack != NULL' failed
Name com.canonical.AppMenu.Registrar does not exist on the session bus
The program 'gkrellm' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadPixmap (invalid Pixmap parameter)'.
  (Details: serial 4092 error_code 4 request_code 56 minor_code 0)
  (Note to programmers: normally, X errors are reported asynchronously;
   that is, you will receive the error a while after causing it.
   To debug your program, run it with the --sync command line
   option to change this behavior. You can then get a meaningful
   backtrace from your debugger if you break on the gdk_x_error() function.)