run_clustering.py crashes when the analyzed software system is small.

[WGC575]

run_clustering.py crashes when the analyzed software system is small. The reason is probably that there is no result generated for identifyMostSimClusters(), and ultimately there is no clustering information available thus causing validation errors.

The error happens for gitlab signald 0.1.0 and other early versions.

This is not a high-priority problem since it only breaks when the analyzed system is too small.