eeschema MacOS - crash in SCH_EDIT_FRAME::SaveCopyForRepeatItem (lp:#1836126)

[Original report](https://bugs.launchpad.net/bugs/1836126) created by **Christian Conkle (conklech)**
```
Trying to place a zero-length wire or bus in eeschema causes a segfault as
of nightly 20190707. I see the same crash in 20190703. I do not see the
same crash in 5.1.2 release.

Two ways to reproduce:

1) Begin drawing a wire or bus with "W" or "B", and then double-click
without moving the cursor.
2) With the draw wire/bus tool active, double-click anywhere in the
schematic.

Relevant part of crash report:

Process:               kicad [61169]
Path:
/private/var/folders/*/kicad.app/Contents/MacOS/kicad
Identifier:            org.kicad-pcb.kicad
Version:               6.0.0-unknown (???)
Code Type:             X86-64 (Native)
Parent Process:        ??? [1]
Responsible:           kicad [61169]
User ID:               502

Date/Time:             2019-07-10 18:53:01.386 -0700
OS Version:            Mac OS X 10.14.5 (18F132)
Report Version:        12
Bridge OS Version:     3.5 (16P5125)
Anonymous UUID:        2F535EFB-DC41-6579-093D-77E72102AE39

Sleep/Wake UUID:       61BB932C-0021-4BC9-B36E-43FD7033E507

Time Awake Since Boot: 98000 seconds
Time Since Wake:       17000 seconds

System Integrity Protection: enabled

Notes:                 Translocated Process

Crashed Thread:        0  Dispatch queue: com.apple.main-thread

Exception Type:        EXC_BAD_ACCESS (SIGSEGV)
Exception Codes:       KERN_INVALID_ADDRESS at 0x0000000000000000
Exception Note:        EXC_CORPSE_NOTIFY

Termination Signal:    Segmentation fault: 11
Termination Reason:    Namespace SIGNAL, Code 0xb
Terminating Process:   exc handler [61169]

VM Regions Near 0:
-->
    __TEXT                 00000001088c2000-0000000108bc4000 [ 3080K]
r-x/rwx SM=COW  /var/folders/*/kicad.app/Contents/MacOS/kicad

Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0   _eeschema.kiface                    0x0000000111977931
SCH_EDIT_FRAME::SaveCopyForRepeatItem(SCH_ITEM*) + 65
1   _eeschema.kiface                    0x0000000111a80bb2
SCH_LINE_WIRE_BUS_TOOL::finishSegments() + 2306
2   _eeschema.kiface                    0x0000000111a7f123
SCH_LINE_WIRE_BUS_TOOL::doDrawSegments(int, SCH_LINE*) + 2003
3   _eeschema.kiface                    0x0000000111a7e625
SCH_LINE_WIRE_BUS_TOOL::DrawSegments(TOOL_EVENT const&) + 469
4   _eeschema.kiface                    0x0000000111a8d945 int
std::__1::__invoke_void_return_wrapper<int>::__call<std::__1::__bind<int
(SCH_LINE_WIRE_BUS_TOOL::*&)(TOOL_EVENT const&), SCH_LINE_WIRE_BUS_TOOL*,
std::__1::placeholders::__ph<1> const&>&, TOOL_EVENT
const&>(std::__1::__bind<int (SCH_LINE_WIRE_BUS_TOOL::*&)(TOOL_EVENT
const&), SCH_LINE_WIRE_BUS_TOOL*, std::__1::placeholders::__ph<1>
const&>&&&, TOOL_EVENT const&&&) + 645
5   _eeschema.kiface                    0x0000000111a8d609
std::__1::__function::__func<std::__1::__bind<int
(SCH_LINE_WIRE_BUS_TOOL::*&)(TOOL_EVENT const&), SCH_LINE_WIRE_BUS_TOOL*,
std::__1::placeholders::__ph<1> const&>,
std::__1::allocator<std::__1::__bind<int
(SCH_LINE_WIRE_BUS_TOOL::*&)(TOOL_EVENT const&), SCH_LINE_WIRE_BUS_TOOL*,
std::__1::placeholders::__ph<1> const&> >, int (TOOL_EVENT
const&)>::operator()(TOOL_EVENT const&) + 57
6   _eeschema.kiface                    0x0000000111dda03e
std::__1::function<int (TOOL_EVENT const&)>::operator()(TOOL_EVENT const&)
const + 142
7   _eeschema.kiface                    0x0000000111dd9f8d COROUTINE<int,
TOOL_EVENT const&>::callerStub(long) + 109
8   _eeschema.kiface                    0x0000000111d22f2a make_fcontext +
42


Version info:

Application: KiCad
Version: (5.1.0-1227-g3db99d65f), debug build
Libraries:
    wxWidgets 3.0.4
    libcurl/7.54.0 LibreSSL/2.6.5 zlib/1.2.11 nghttp2/1.24.1
Platform: Mac OS X (Darwin 18.6.0 x86_64), 64 bit, Little endian, wxMac
Build Info:
    wxWidgets: 3.0.4 (wchar_t,STL containers,compatible with 2.8)
    Boost: 1.69.0
    OpenCASCADE Community Edition: 6.9.1
    Curl: 7.54.0
    Compiler: Clang 9.0.0 with C++ ABI 1002

Build settings:
    KICAD_SCRIPTING=ON
    KICAD_SCRIPTING_MODULES=ON
    KICAD_SCRIPTING_PYTHON3=OFF
    KICAD_SCRIPTING_WXPYTHON=ON
    KICAD_SCRIPTING_WXPYTHON_PHOENIX=OFF
    KICAD_SCRIPTING_ACTION_MENU=ON
    BUILD_GITHUB_PLUGIN=ON
    KICAD_USE_OCE=ON
    KICAD_USE_OCC=OFF
    KICAD_SPICE=ON
```
Original tags: eeschema macos

Story points: 6.0