Quickly selecting multiple columns/rows in Pin Table dialog causes assert (fixed in wxWidgets 3.1.2) (lp:#1794013)

[Original report](https://bugs.launchpad.net/bugs/1794013) created by **Paul Hansel (paulhansel)**
```
Occurs on any symbol's pin table.

ASSERT INFO:
../src/generic/grid.cpp(4054): assert "!m_winCapture" failed in
DoGridDragEvent(): shouldn't capture the mouse twice

BACKTRACE:
[1] wxGrid::DoGridDragEvent(wxMouseEvent&, wxGridCellCoords const&)
[2] wxGrid::ProcessGridCellMouseEvent(wxMouseEvent&)
[3] wxAppConsoleBase::CallEventHandler(wxEvtHandler*, wxEventFunctor&,
wxEvent&) const
[4] wxEvtHandler::ProcessEventIfMatchesId(wxEventTableEntryBase const&,
wxEvtHandler*, wxEvent&)
[5] wxEventHashTable::HandleEvent(wxEvent&, wxEvtHandler*)
[6] wxEvtHandler::TryHereOnly(wxEvent&)
[7] wxEvtHandler::ProcessEventLocally(wxEvent&)
[8] wxEvtHandler::ProcessEvent(wxEvent&)
[9] wxEvtHandler::SafelyProcessEvent(wxEvent&)
[10] g_closure_invoke
[11] g_signal_emit_valist
[12] g_signal_emit
[13] gtk_propagate_event
[14] gtk_main_do_event
[15] g_main_context_dispatch
[16] g_main_loop_run
[17] gtk_main
[18] wxGUIEventLoop::DoRun()
[19] wxEventLoopBase::Run()
[20] wxDialog::ShowModal()
[21] wxAppConsoleBase::CallEventHandler(wxEvtHandler*, wxEventFunctor&,
wxEvent&) const
[22] wxEvtHandler::ProcessEventIfMatchesId(wxEventTableEntryBase const&,
wxEvtHandler*, wxEvent&)
[23] wxEventHashTable::HandleEvent(wxEvent&, wxEvtHandler*)
[24] wxEvtHandler::TryHereOnly(wxEvent&)
[25] wxEvtHandler::DoTryChain(wxEvent&)
[26] wxEvtHandler::ProcessEvent(wxEvent&)
[27] wxWindowBase::TryAfter(wxEvent&)
[28] wxAuiToolBar::OnLeftUp(wxMouseEvent&)
[29] wxAppConsoleBase::CallEventHandler(wxEvtHandler*, wxEventFunctor&,
wxEvent&) const
[30] wxEvtHandler::ProcessEventIfMatchesId(wxEventTableEntryBase const&,
wxEvtHandler*, wxEvent&)
[31] wxEventHashTable::HandleEvent(wxEvent&, wxEvtHandler*)
[32] wxEvtHandler::TryHereOnly(wxEvent&)
[33] wxEvtHandler::ProcessEventLocally(wxEvent&)
[34] wxEvtHandler::ProcessEvent(wxEvent&)
[35] wxEvtHandler::SafelyProcessEvent(wxEvent&)
[36] g_closure_invoke
[37] g_signal_emit_valist
[38] g_signal_emit
[39] gtk_propagate_event
[40] gtk_main_do_event
[41] g_main_context_dispatch
[42] g_main_loop_run
[43] gtk_main
[44] wxGUIEventLoop::DoRun()
[45] wxEventLoopBase::Run()
[46] wxAppConsoleBase::MainLoop()
[47] APP_KICAD::OnRun()
[48] wxEntry(int&, wchar_t**)
[49] main
[50] __libc_start_main
[51] _start


Version:

Application: kicad
Version: (6.0.0-rc1-dev-576-gae13e44), release build
Libraries:
    wxWidgets 3.0.2
    libcurl/7.47.0 OpenSSL/1.0.2g zlib/1.2.8 libidn/1.32 librtmp/2.3
Platform: Linux 4.4.0-135-generic x86_64, 64 bit, Little endian, wxGTK
Build Info:
    wxWidgets: 3.0.2 (wchar_t,wx containers,compatible with 2.8) GTK+ 2.24
    Boost: 1.58.0
    OpenCASCADE Community Edition: 6.8.0
    Curl: 7.47.0
    Compiler: GCC 5.4.0 with C++ ABI 1009

Build settings:
    USE_WX_GRAPHICS_CONTEXT=OFF
    USE_WX_OVERLAY=OFF
    KICAD_SCRIPTING=ON
    KICAD_SCRIPTING_MODULES=ON
    KICAD_SCRIPTING_WXPYTHON=ON
    KICAD_SCRIPTING_ACTION_MENU=OFF
    BUILD_GITHUB_PLUGIN=ON
    KICAD_USE_OCE=ON
    KICAD_USE_OCC=OFF
    KICAD_SPICE=ON
```
Original tags: eeschema wxwidgets

Story points: 6.0