fixed custom templates location for nodejs generator

Author: HugoMario

src/main/java/io/swagger/codegen/v3/generators/nodejs/NodeJSServerCodegen.java

@@ -288,7 +288,9 @@ public void processOpts() {
          * Template Location.  This is the location which templates will be read from.  The generator
          * will use the resource stream to attempt to read the templates.
          */
-        embeddedTemplateDir = templateDir = getTemplateDir();
+        if (StringUtils.isBlank(templateDir)) {
+            embeddedTemplateDir = templateDir = getTemplateDir();
+        }
 
         if (additionalProperties.containsKey(GOOGLE_CLOUD_FUNCTIONS)) {
             setGoogleCloudFunctions(