Fix: CIccTagSpectralViewingConditions() UB

[ChrisCoxArt]

Fixes #216

[xsscx]

PR 225 Repro

          export CXX=clang++
          git clone https://github.com/InternationalColorConsortium/iccDEV.git
          cd iccDEV
          git fetch origin pull/225/head:pr-225
          git checkout pr-225
          cd Build
          cmake -DCMAKE_INSTALL_PREFIX=$HOME/.local -DCMAKE_BUILD_TYPE=Debug -Wno-dev -DCMAKE_CXX_FLAGS="-g -fsanitize=address,undefined -fno-omit-frame-pointer -Wall" -DENABLE_TOOLS=ON -DENABLE_STATIC_LIBS=ON -DENABLE_SHARED_LIBS=ON Cmake/
          make -j$(nproc)
          echo "========= BEGIN INSIDE STUB for Issue 216 ========="
          cd ../Testing/
          echo "=== Updating PATH ==="
           for d in ../Build/Tools/*; do
            [ -d "$d" ] && export PATH="$(realpath "$d"):$PATH"
           done
          echo "========= fetching the profile... =========" 
          wget https://github.com/xsscx/Commodity-Injection-Signatures/raw/refs/heads/master/graphics/icc/Cat8Lab-D65_2degMeta.icc
          iccRoundTrip Cat8Lab-D65_2degMeta.icc

Expected Output

2025-11-24 18:07:45 (12.7 MB/s) - ‘Cat8Lab-D65_2degMeta.icc’ saved [2600/2600]

Profile:          'Cat8Lab-D65_2degMeta.icc'
Rendering Intent: Relative Colorimetric
Specified Gamut:  Not Specified

Round Trip 1
------------
Min DeltaE:        0.00
Mean DeltaE:       0.00
Max DeltaE:        0.00

Max L, a, b:   0.000000, -128.000000, -128.000000

Round Trip 2
------------
Min DeltaE:        0.00
Mean DeltaE:       0.00
Max DeltaE:        0.00

Max L, a, b:   0.000000, -128.000000, -128.000000

PRMG Interoperability - Round Trip Results
------------------------------------------------------
DE <= 1.0 (  201613): 100.0%
DE <= 2.0 (  201613): 100.0%
DE <= 3.0 (  201613): 100.0%
DE <= 5.0 (  201613): 100.0%
DE <=10.0 (  201613): 100.0%
Total     (  201613)

The above Test indicates that PR225 resolves Issue 216 and this PR will be Merged.

Thank You @ChrisCoxArt for your time & efforts!
PR225 addressed the UB in CIccTagSpectralViewingConditions::CIccTagSpectralViewingConditions() reported from Issue 216
Signed-off-by: D Hoyt xss@xss.cx

[xsscx]

GHSA-fg9m-j9x8-8279