fix(timer_module): Ensure that interval > 0 (#2274)

Since 3.5.0, we use m_interval for a modulo operation, this crashes the
bar if the interval is 0. A non-positive interval shouldn't be allowed
anyway, so we now throw an exception in that case.

Fixes #2273

src/modules/github.cpp

@@ -23,7 +23,7 @@ namespace modules {
       m_api_url += '/';
     }
 
-    m_interval = m_conf.get<decltype(m_interval)>(name(), "interval", 60s);
+    set_interval(60s);
     m_empty_notifications = m_conf.get(name(), "empty-notifications", m_empty_notifications);
 
     m_formatter->add(DEFAULT_FORMAT, TAG_LABEL, {TAG_LABEL});