Handle nameless modules during bp2build conversion.

So far it is `package` module.

Test: treehugger
Change-Id: Ibf3af0b0bf0a532e2ea1d478275a5ac3784ef170
diff --git a/bp2build/testing.go b/bp2build/testing.go
index ac1268c..ee9200a 100644
--- a/bp2build/testing.go
+++ b/bp2build/testing.go
@@ -429,7 +429,9 @@
 	}
 
 	attrStrings := make([]string, 0, len(attrs)+1)
-	attrStrings = append(attrStrings, fmt.Sprintf(`    name = "%s",`, name))
+	if name != "" {
+		attrStrings = append(attrStrings, fmt.Sprintf(`    name = "%s",`, name))
+	}
 	for _, k := range android.SortedStringKeys(attrs) {
 		attrStrings = append(attrStrings, fmt.Sprintf("    %s = %s,", k, attrs[k]))
 	}