Regenerate index if `StoreIdentityCids` is enabled and existing index does not have `FullyIndexed` characteristic

[masih]

ReadOrGenerateIndex does not re-generate index if the existing index doesn't satisfy passed options.

go-car/v2/index_gen.go

Lines 146 to 149 in f437812

	// If index is present, then no need to generate; decode and return it.
	if v2r.Header.HasIndex() {
	return index.ReadFrom(v2r.IndexReader())
	}