fix: guard against whitespace-only type attribute panic in ParseReleaseGroups

internal/musicbrainz/client.go

@@ -148,7 +148,9 @@ func ParseReleaseGroups(data []byte) (*ParsedReleaseGroups, error) {
 		// so take the first token as the primary type.
 		primary := rg.PrimaryType
 		if primary == "" && rg.TypeAttr != "" {
-			primary = strings.Fields(rg.TypeAttr)[0]
+			if fields := strings.Fields(rg.TypeAttr); len(fields) > 0 {
+				primary = fields[0]
+			}
 		}
 		result.ReleaseGroups = append(result.ReleaseGroups, ReleaseGroup{
 			ID:             rg.ID,