create corner not working properly in modedit (lp:#1853726)

[Original report](https://bugs.launchpad.net/bugs/1853726) created by **Clayton White (clayton13)**
```
Hi,

When using create corner on a line segment the line is split visually as
expected in the viewer; however, when a segment is selected and moved it
immediately transforms into the original segment.

It appears that create corner is not being applied properly to the new
segments, the effects can be seen immediately in the viewer by attempting
to manipulate the segment or through a save and reopen process.

For example, if create corner is used on a segment, 2 segments can be seen.
However, when saved and reopened the original segment is duplicated instead
of 2 new sub-segments.

To replicate:
Create a new footprint.
Create a line (on any layer) ie (0,0)->(0,3).
Use create corner to split the line at (0,1).
Save. Reopen.
The result will be two identical lines (0,0)->(0,3). Instead of
(0,0)->(0,1) and (0,1)->(0,3).

Please see .kicad_mod exports below.

Original: before create corner
(module "mylib:test" (layer F.Cu) (tedit 5DDA0BB8)
  (fp_text reference "REF**" (at 3.81 -2.54 unlocked) (layer F.SilkS)
    (effects (font (size 1 1) (thickness 0.15)))
  )
  (fp_text value "test" (at 0 -2.54 unlocked) (layer F.Fab)
    (effects (font (size 1 1) (thickness 0.15)))
  )
  (fp_line (start 0 0) (end 3 0) (layer F.SilkS) (width 0.12))
)

Result: after create corner at (0,3)
(module "mylib:test" (layer F.Cu) (tedit 5DDA0BCB)
  (fp_text reference "REF**" (at 3.81 -2.54 unlocked) (layer F.SilkS)
    (effects (font (size 1 1) (thickness 0.15)))
  )
  (fp_text value "test" (at 0 -2.54 unlocked) (layer F.Fab)
    (effects (font (size 1 1) (thickness 0.15)))
  )
  (fp_line (start 0 0) (end 3 0) (layer F.SilkS) (width 0.12))
  (fp_line (start 0 0) (end 3 0) (layer F.SilkS) (width 0.12))
)



Tested on the following builds:

Application: ModEdit
Version: 5.1.5-52549c5~84~ubuntu18.04.1, release build
Libraries:
    wxWidgets 3.0.4
    libcurl/7.58.0 OpenSSL/1.1.1 zlib/1.2.11 libidn2/2.0.4 libpsl/0.19.1
(+libidn2/2.0.4) nghttp2/1.30.0 librtmp/2.3
Platform: Linux 4.15.0-47-generic x86_64, 64 bit, Little endian, wxGTK
Build Info:
    wxWidgets: 3.0.4 (wchar_t,wx containers,compatible with 2.8) GTK+ 3.22
    Boost: 1.65.1
    OpenCASCADE Community Edition: 6.9.1
    Curl: 7.58.0
    Compiler: GCC 7.4.0 with C++ ABI 1011

Build settings:
    USE_WX_GRAPHICS_CONTEXT=OFF
    USE_WX_OVERLAY=ON
    KICAD_SCRIPTING=ON
    KICAD_SCRIPTING_MODULES=ON
    KICAD_SCRIPTING_PYTHON3=ON
    KICAD_SCRIPTING_WXPYTHON=ON
    KICAD_SCRIPTING_WXPYTHON_PHOENIX=ON
    KICAD_SCRIPTING_ACTION_MENU=ON
    BUILD_GITHUB_PLUGIN=ON
    KICAD_USE_OCE=ON
    KICAD_USE_OCC=OFF
    KICAD_SPICE=ON


Application: ModEdit
Version: 5.99.0-unknown-3be1862~100~ubuntu18.04.1, release build
Libraries:
    wxWidgets 3.0.4
    libcurl/7.58.0 OpenSSL/1.1.1 zlib/1.2.11 libidn2/2.0.4 libpsl/0.19.1
(+libidn2/2.0.4) nghttp2/1.30.0 librtmp/2.3
Platform: Linux 4.15.0-47-generic x86_64, 64 bit, Little endian, wxGTK
Build Info:
    Build date: Nov 21 2019 00:31:52
    wxWidgets: 3.0.4 (wchar_t,wx containers,compatible with 2.8) GTK+ 3.22
    Boost: 1.65.1
    OpenCASCADE Community Edition: 6.9.1
    Curl: 7.58.0
    Compiler: GCC 7.4.0 with C++ ABI 1011

Build settings:
    KICAD_SCRIPTING=ON
    KICAD_SCRIPTING_MODULES=ON
    KICAD_SCRIPTING_PYTHON3=ON
    KICAD_SCRIPTING_WXPYTHON=ON
    KICAD_SCRIPTING_WXPYTHON_PHOENIX=ON
    KICAD_SCRIPTING_ACTION_MENU=ON
    BUILD_GITHUB_PLUGIN=ON
    KICAD_USE_OCE=ON
    KICAD_USE_OCC=OFF
    KICAD_SPICE=ON
```
Original tags: pcbnew

Story points: 10.0