Editor crash on right click into sequence area

[westram]

• reproduce: unknown
• effect: complete ARB frozen (maybe crashed inside TA)
• backtrace:

  -------------------- ARB-backtrace 'received signal 11':
  /boar4/wl/comp_arb_boar4/myARB/lib/libCORE.so(GBK_dump_backtrace(_IO_FILE*, char const*)+0x34)[0x7f7f282801a4]
  /boar4/wl/comp_arb_boar4/myARB/lib/libCORE.so(+0xe432)[0x7f7f28281432]
  /lib64/libc.so.6(+0x34da0)[0x7f7f25503da0]
  arb_edit4(ED4_base::get_parent(ED4_level) const+0x0)[0x484080]
  arb_edit4(ED4_setColumnblockCorner(AW_event*, ED4_sequence_terminal*)+0x6b7)[0x45a0e7]
  arb_edit4(ED4_terminal::event_sent_by_parent(AW_event*, AW_window*)+0xb8)[0x490aa8]
  arb_edit4(ED4_manager::event_sent_by_parent(AW_event*, AW_window*)+0xac)[0x47ef6c]
  arb_edit4(ED4_manager::event_sent_by_parent(AW_event*, AW_window*)+0xac)[0x47ef6c]
  [...]
  arb_edit4(ED4_manager::event_sent_by_parent(AW_event*, AW_window*)+0xac)[0x47ef6c]
  arb_edit4(ED4_manager::event_sent_by_parent(AW_event*, AW_window*)+0xac)[0x47ef6c]
  arb_edit4(ED4_input_cb(AW_window*)+0x1dc)[0x46954c]
  /boar4/wl/comp_arb_boar4/myARB/lib/libWINDOW.so(AW_cb::run_callbacks()+0xa7)[0x7f7f27dc8097]
  /usr/lib64/libXt.so.6(XtCallCallbackList+0x12e)[0x7f7f2747790e]
  /usr/lib64/libXm.so.4(_XmDrawingAreaInput+0x13b)[0x7f7f27987a6b]
  /usr/lib64/libXt.so.6(+0x4a40d)[0x7f7f274ac40d]
  /usr/lib64/libXt.so.6(+0x4a861)[0x7f7f274ac861]
  /usr/lib64/libXt.so.6(_XtTranslateEvent+0x62d)[0x7f7f274ad5fd]
  /usr/lib64/libXt.so.6(XtDispatchEventToWidget+0x40b)[0x7f7f27485b3b]
  /usr/lib64/libXt.so.6(+0x2428e)[0x7f7f2748628e]
  /usr/lib64/libXt.so.6(XtDispatchEvent+0xb4)[0x7f7f27486354]
  /usr/lib64/libXt.so.6(XtAppProcessEvent+0x2c9)[0x7f7f27492079]
  /usr/lib64/libXt.so.6(XtAppMainLoop+0x2d)[0x7f7f274867cd]
  arb_edit4(ARB_main(int, char**)+0x65f)[0x46d33f]
  /lib64/libc.so.6(__libc_start_main+0xf5)[0x7f7f254f0455]
  arb_edit4[0x44a039]
  -------------------- End of backtrace
  [Terminating with signal 11]