pcbnew: user driven trackwidth change should override "use trackwidth from previous segment" button
# Description
User is not able to control trackwidth for first track segment using hotkeys if this button  is activated. In certain circumstances, this button prevents user to start routing at all. User should be able to control trackwidth anytime by using hotkeys.

# Steps to reproduce
1. open: [noname_2_pr.7z](/uploads/2885c96fd15360dd71d57b6e9e3a3d6f/noname_2_pr.7z)
2. Start placing track over any pad which has track already routed to it;
3. New track is placed with trackwidth driven by existing track, this is ok, because button  is active;
4. Press shift + W (decrease trackwidth).
5. Trackwidth is not changed, but GUI indicates that change.
It is expected to control trackwidth any time, ignoring the state of  button. This button should propose initial width of the segment, nut should be overridden by user actions (pressing hotkeys).
Also, note how 2nd segment width is changed (in the video end). This does not correlate to behavior of the 1st segment.
* This is tightly related to the following problem: #6984 (maybe more eyes will see it).
# KiCad Version
<!-- Copy version information (from main menu Help->About KiCad ->Copy Version Info) and paste it between the triple backticks below to preserve the formatting. -->
```
Application: KiCad PCB Editor (64-bit)
Version: (5.99.0-10962-gfbc135e69f), release build
Libraries:
wxWidgets 3.1.5
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: Jun 10 2021 21:00:20
wxWidgets: 3.1.5 (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_USE_OCC=ON
KICAD_SPICE=ON
```
issue