HSL color selector: Lightness '0', '255' resets Hue and Saturation to '0' (rev >= 14160)

[su_v]

Steps to reproduce:
1) launch trunk with default (new) prefs, default new doc (en_US)
2) draw a rect (-> default fill: blue)
2) open 'Fill and Stroke'
3) switch to the HSL tab for the fill color
4) drag lightness slider 'L' to '0' (or '255')

Expected result: only 'L' changes, 'H' and 'S' remain unchanged.
Actual result: both 'H' and 'S' are reset to '0'.

Reproduced with latest trunk Inkscape 0.91+devel r14758 (on OS X 10.7.5).

Based on tests with archived builds:
- not reproduced with any stable release (0.47, 0.48, 0.91)
- not reproduced with 0.91+devel rev <= 14159
- reproduced with 0.91+devel rev >= 14165;
this change was likely introduced with the changes in rev 14160:
https://bazaar.launchpad.net/~inkscape.dev/inkscape/trunk/changes/14165
Rev 14160: Merge in Tomasz's fill-n-stroke-cppify branch
https://bazaar.launchpad.net/~inkscape.dev/inkscape/trunk/revision/14160

Related earlier reports:
* A different regression introduced with rev 14160:
Bug #1462907 “Color wheel: can't rotate while on black”
* Similar behavior introduced earlier in 0.48:
Bug #1249618 “Color wheel changes hue when picking brightness and saturation”
Bug #1565261 “HSL color selector: saturation '0' resets Hue to '0' (>= 0.48)”

[jazzynico (jazzynico)]

Reproduced on Windows 7, Inkscape trunk rev. 14761.

[jazzynico (jazzynico)]

Also reproduced on Xubuntu 16.04, Inkscape trunk rev. 15095.

[Qantas94Heavy (qantas94heavy)]

Can still reproduce with Inkscape 1.0alpha (2019-03-21, 75da9ac4ea).

[Nathan Lee (nathan.lee)]

Closing as part of the bug migration.

Issue is still present in master, but issue has been migrated to https://gitlab.com/inkscape/inbox/issues/1412