New day cycle key frames cannot be saved

[canny]

Noticed on a Firestorm 7.1.13 test version but the same thing happens on the latest SL Viewer release as well. When editing a day cycle and adding new key frames, apparently everything works correctly. After saving the day cycle, however, all the newly added key frames are lost. This is very inconvenient after spending quite some time adding new key frames and setting them up, only to have them vanish.

Steps to reproduce:

1: Create a new day cycle or copy or edit an existing one

2: Add new key frames anywhere

3: Save the day cycle

4: Open it again

5: Newly added key frames won't be there

https://secondlife.canny.io/admin/board/bug-reports/p/new-day-cycle-key-frames-cannot-be-saved

[canny]

This issue has been linked to a Canny post: New day cycle key frames cannot be saved 🎉

[Hecklezz]

This issue was introduced in the same PR that broke the Sky Ambient colour blending discussed in this issue which has since been fixed-
#4185

The culprit PR-
#2545

[Hecklezz]

The issue is that new frames added by the Add Sky button is failing in LLSettingsBase::validate() and as a result doesn't get added to the LLSettingsVODay::buildClone() that is used when clicking save.
The 3 settings which are failing are-
'rayleigh_config'
'absorption_config'
'mie_config'

[Hecklezz]

Those 3 mentioned above are getting set to null here-

viewer/indra/llinventory/llsettingssky.cpp

Line 667 in 2c35cdd

mAbsorptionConfigs = interpolateSDMap(mAbsorptionConfigs, other->mAbsorptionConfigs, defaults, blendf, skip, slerps);

viewer/indra/llinventory/llsettingssky.cpp

Line 668 in 2c35cdd

mMieConfigs = interpolateSDMap(mMieConfigs, other->mMieConfigs, defaults, blendf, skip, slerps);

viewer/indra/llinventory/llsettingssky.cpp

Line 669 in 2c35cdd

mRayleighConfigs = interpolateSDMap(mRayleighConfigs, other->mRayleighConfigs, defaults, blendf, skip, slerps);

interpolateSDMap is never interpolating and combining the current and other configs for those 3, resulting in them becoming null, and then later when they are validated, they are empty resulting in the sky never being saved into the day cycle.

This happens because they are aren't actually maps, they are arrays with maps inside, so the function doesn't interpret them correctly as maps.

Edit: PR with potential fix here-
#4227