pcbnew, gal: track tool cancels at pressing Del hotkey

[Sergey A. Borshch]

Steps to reproduce:
1) select "Run push and shove router (single tracks)" (X hotkey)
2) place track.
3) double-click to complete track.
4) place mouse cursor over track segment and press "Del" key to delete segment.

Expected behavior: "Run push and shove router (single tracks)" tool stays selected to continue placing tracks.
Actual behavior: "Run push and shove router (single tracks)" tool cancels and selection tool activated, user has to move mouse and select router tool again after every wrong placed segment delete.

Version info: today's git head:
Application: Pcbnew
Version: (5.99.0-169-gce62941bb), release build
Libraries:
    wxWidgets 3.0.4
Platform: Linux 5.0.0-23-generic x86_64, 64 bit, Little endian, wxGTK
Build Info:
    Build date: Sep 29 2019 13:17:54
    wxWidgets: 3.0.4 (wchar_t,wx containers,compatible with 2.8) GTK+ 2.24
    Boost: 1.65.1
    Compiler: GCC 7.4.0 with C++ ABI 1011

Build settings:
    KICAD_SCRIPTING=OFF
    KICAD_SCRIPTING_MODULES=OFF
    KICAD_SCRIPTING_PYTHON3=OFF
    KICAD_SCRIPTING_WXPYTHON=OFF
    KICAD_SCRIPTING_WXPYTHON_PHOENIX=OFF
    KICAD_SCRIPTING_ACTION_MENU=OFF
    BUILD_GITHUB_PLUGIN=OFF
    KICAD_USE_OCE=OFF
    KICAD_USE_OCC=OFF
    KICAD_SPICE=ON