properties panel: extra unwanted minus-sign added

Description

Under some circumstances the properties panel adds a additional untyped minus-character. (most probably from an earlier typed negative value).

This happens reproducible with the steps below.

affects also v799.

Steps to reproduce

1. open any board (or the attached project: propertiespanel_textitem.zip
2. add a simple textitem near the 0,0 coordinate
3. use the properties panel for the next steps
4. set "Position y" to -10, ENTER (text should move some mm down)
5. click into Orientation field, type "20", ENTER
6. notice: the orientation accepts the value "-20", thus adding autonomous a negative sign.
7. Is this the first operation of a newly added AI?

2023-03-04_12-07-51

KiCad Version

Application: KiCad PCB Editor x64 on x64

Version: (7.0.0-160-g9b61b350fe), release build

Libraries:
	wxWidgets 3.2.2
	FreeType 2.12.1
	HarfBuzz 5.0.1
	FontConfig 2.14.1

Platform: Windows 10 (build 19044), 64-bit edition, 64 bit, Little endian, wxMSW

	wxWidgets: 3.2.2 (wchar_t,wx containers)
	Boost: 1.80.0
	OCC: 7.6.2
	Curl: 7.83.1-DEV
	ngspice: 39
	Compiler: Visual C++ 1934 without C++ ABI

Build settings:
	KICAD_SPICE=ON