pcbnew: Predefined wire sizes entry list bug

Description

3334C

Steps to reproduce

1. File -> Board setup -> Pre-defined sizes
2. Enter wire sizes from 0.2 .. 0.32 in 0.1 mm steps.
3. First symbols do not appear in entry fields, as seen in the video.

In case nothing bad happens after step 2, close and reopen dialog after step 2, try to enter next sizes after reopening.

Or, just keep clicking on existing list:

39300

KiCad Version

Application: KiCad PCB Editor

Version: (5.99.0-10363-ga7f956581c), release build

Libraries:
	wxWidgets 3.1.4
	libcurl/7.74.0-DEV Schannel zlib/1.2.11

Platform: Windows 10 (build 19042), 64-bit edition, 64 bit, Little endian, wxMSW

Build Info:
	Date: Apr 20 2021 12:03:29
	wxWidgets: 3.1.4 (wchar_t,STL containers)
	Boost: 1.75.0
	OCC: 7.5.0
	Curl: 7.74.0-DEV
	ngspice: 34
	Compiler: Visual C++ 1928 without C++ ABI

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
	KICAD_USE_OCC=ON
	KICAD_SPICE=ON