[FIX] email_template: format tz, do no display tz if none set

When displaying the datetime according to the lang in the context

Otherwise, it displays '(False)' at the end of the datetime

addons/email_template/email_template.py

@@ -60,7 +60,7 @@ def format_tz(pool, cr, uid, dt, tz=False, format=False, context=None):
 
         fdate = ts.strftime(format_date)
         ftime = ts.strftime(format_time)
-        return "%s %s (%s)" % (fdate, ftime, tz)
+        return "%s %s%s" % (fdate, ftime, (' (%s)' % tz) if tz else '')
 
 try:
     # We use a jinja2 sandboxed environment to render mako templates.