Carla: Fix some compiler warnings

c++/carla-includes/lv2/event-helpers.h

@@ -148,7 +148,7 @@ lv2_event_get(LV2_Event_Iterator* iter,
               uint8_t**           data)
 {
 	if (!lv2_event_is_valid(iter)) {
-		return false;
+		return nullptr;
 	}
 
 	LV2_Event* const ev = (LV2_Event*)(

c++/carla-plugin/carla_bridge.cpp

@@ -994,7 +994,7 @@ CarlaPlugin* CarlaPlugin::newBridge(const initializer& init, BinaryType btype, P
     if (! extra)
     {
         init.engine->setLastError("Bridge not possible, bridge-binary not found");
-        return false;
+        return nullptr;
     }
 
     short id = init.engine->getNewPluginId();