camera trigger: do not try to start if interface was not created

Signed-off-by: RomanBapst <bapstroman@gmail.com>

src/drivers/camera_trigger/camera_trigger.cpp

@@ -133,7 +133,7 @@ class CameraTrigger : public px4::ScheduledWorkItem
 	/**
 	 * Start the task.
 	 */
-	void		start();
+	bool		start();
 
 	/**
 	 * Stop the task.
@@ -427,9 +427,17 @@ CameraTrigger::shoot_once()
 	}
 }
 
-void
+bool
 CameraTrigger::start()
 {
+	if (_camera_interface == nullptr) {
+		if (camera_trigger::g_camera_trigger != nullptr) {
+			delete (camera_trigger::g_camera_trigger);
+		}
+
+		return false;
+	}
+
 	if ((_trigger_mode == TRIGGER_MODE_INTERVAL_ALWAYS_ON ||
 	     _trigger_mode == TRIGGER_MODE_DISTANCE_ALWAYS_ON) &&
 	    _camera_interface->has_power_control() &&
@@ -456,6 +464,8 @@ CameraTrigger::start()
 
 	// start to monitor at high rate for trigger enable command
 	ScheduleNow();
+
+	return true;
 }
 
 void
@@ -827,7 +837,11 @@ int camera_trigger_main(int argc, char *argv[])
 			return 1;
 		}
 
-		camera_trigger::g_camera_trigger->start();
+		if (!camera_trigger::g_camera_trigger->start()) {
+			PX4_WARN("failed to start camera trigger");
+			return 1;
+		}
+
 		return 0;
 	}