Skip MQTT allocation when disabled (#10411)

Co-authored-by: Ben Meadors <benmmeadors@gmail.com>

src/mqtt/MQTT.cpp

@@ -409,6 +409,9 @@ void MQTT::onReceive(char *topic, byte *payload, size_t length)
 
 void mqttInit()
 {
+    if (!moduleConfig.mqtt.enabled)
+        return;
+
     new MQTT();
 }
 

test/test_mqtt/MQTT.cpp

@@ -800,6 +800,17 @@ void test_disabled(void)
     TEST_ASSERT_FALSE(mqtt->isEnabled());
 }
 
+void test_mqttInitSkipsAllocationWhenDisabled(void)
+{
+    delete unitTest;
+    mqtt = unitTest = NULL;
+
+    moduleConfig.mqtt.enabled = false;
+    mqttInit();
+
+    TEST_ASSERT_NULL(mqtt);
+}
+
 // Subscriptions contain the moduleConfig.mqtt.root prefix.
 void test_customMqttRoot(void)
 {
@@ -912,6 +923,7 @@ void setup()
     RUN_TEST(test_usingCustomServer);
     RUN_TEST(test_enabled);
     RUN_TEST(test_disabled);
+    RUN_TEST(test_mqttInitSkipsAllocationWhenDisabled);
     RUN_TEST(test_customMqttRoot);
     RUN_TEST(test_configEmptyIsValid);
     RUN_TEST(test_configEnabledEmptyIsValid);