fix issues in --reset-values and --reuse-values on helm v3 (#160)

Correction of #159

Author: jonasrutishauser

cmd/helm3.go

@@ -65,7 +65,7 @@ func (d *diffCmd) template() ([]byte, error) {
 	// Helm automatically enable --reuse-values when there's no --set, --set-string, --set-values, --set-file present.
 	// Let's simulate that in helm-diff.
 	// See https://medium.com/@kcatstack/understand-helm-upgrade-flags-reset-values-reuse-values-6e58ac8f127e
-	shouldDefaultReusingValues := len(d.values) > 0 && len(d.stringValues) > 0 && len(d.valueFiles) > 0 && len(d.fileValues) > 0
+	shouldDefaultReusingValues := len(d.values) == 0 && len(d.stringValues) == 0 && len(d.valueFiles) == 0 && len(d.fileValues) == 0
 	if (d.reuseValues || shouldDefaultReusingValues) && !d.resetValues {
 		tmpfile, err := ioutil.TempFile("", "existing-values")
 		if err != nil {