[FIX] sms: prevent crash when previewing template without records

This commit fixes the traceback while previewing SMS template when there
are no records available.

TaskID 2180132
PR #44080

Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>

addons/sms/wizard/sms_template_preview.py

@@ -53,4 +53,4 @@ class SMSTemplatePreview(models.TransientModel):
             self.res_id = self.resource_ref.id
         if self.sms_template_id:
             template = self.sms_template_id.with_context(lang=self.lang)
-            self.body = template._render_template(template.body, template.model, self.res_id or 0)
+            self.body = template._render_template(template.body, template.model, self.res_id or 0) if self.resource_ref else template.body