[Users] python plugin crash

[Igor Mammedov]

I'm testing out gkt3 branch and python plugin in Fedora32 with the goal to make add_mark_thread_read_menu_item() from examples work.

However it doen't work, after some tinkering problem was isolated to executing
  clawsmail.get_mainwindow_action_group()
in python console, which SIGSEGVs with following backtrace:
  
(gdb) bt
#0  0x00007fffe53fb752 in get_gobj_from_address (addr=<optimized out>) at clawsmailmodule.c:64
#1  0x00007fffe517994d in cfunction_vectorcall_NOARGS () at /lib64/libpython3.8.so.1.0
#2  0x00007fffe51724d7 in _PyEval_EvalFrameDefault () at /lib64/libpython3.8.so.1.0
#3  0x00007fffe517b2b8 in function_code_fastcall () at /lib64/libpython3.8.so.1.0
#4  0x00007fffe516d744 in _PyEval_EvalFrameDefault () at /lib64/libpython3.8.so.1.0
#5  0x00007fffe516c231 in _PyEval_EvalCodeWithName () at /lib64/libpython3.8.so.1.0
#6  0x00007fffe51e71c9 in PyEval_EvalCodeEx () at /lib64/libpython3.8.so.1.0
#7  0x00007fffe51e718b in PyEval_EvalCode () at /lib64/libpython3.8.so.1.0
#8  0x00007fffe5207c98 in run_eval_code_obj () at /lib64/libpython3.8.so.1.0
#9  0x00007fffe52073c3 in run_mod () at /lib64/libpython3.8.so.1.0
#10 0x00007fffe50f3a62 in PyRun_FileExFlags () at /lib64/libpython3.8.so.1.0
#11 0x00007fffe50f33fe in PyRun_SimpleFileExFlags () at /lib64/libpython3.8.so.1.0
#12 0x00007fffe53fde16 in run_script_file (filename=0xd14550 "/home/xxx/.claws-mail/python-scripts/auto/startup", compose=0x0) at python_plugin.c:188
#13 0x00007fffe53fe94b in run_auto_script_file_if_it_exists (autofilename=<optimized out>, compose=0x0) at python_plugin.c:202
#14 0x00007fffe53ff1d9 in plugin_init (error=<optimized out>) at python_plugin.c:720
#15 0x00000000005d451f in plugin_load (filename=0x7fffffffb200 "/usr/local/lib/claws-mail/plugins/python.so", error=0x7fffffffb1f8) at plugin.c:516
#16 0x00000000005d4b27 in plugin_load_all (type=type at entry=0x642f88 "GTK3") at plugin.c:616
#17 0x0000000000445282 in main (argc=<optimized out>, argv=<optimized out>) at main.c:1480