Handle empty symmetric coloring patterns

[blegat]

Detecting when working on jump-dev/MathOptInterface.jl#3105

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 43.89%. Comparing base (f233ebc) to head (1fa90cb).

Files with missing lines	Patch %	Lines
src/postprocessing.jl	0.00%	1 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (f233ebc) and HEAD (1fa90cb). Click for more details.

HEAD has 4 uploads less than BASE

Flag	BASE (f233ebc)	HEAD (1fa90cb)
	5	1

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #352       +/-   ##
===========================================
- Coverage   99.76%   43.89%   -55.88%     
===========================================
  Files          22       20        -2     
  Lines        2541     2488       -53     
===========================================
- Hits         2535     1092     -1443     
- Misses          6     1396     +1390     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.