AP_Scripting: CAN: get_device and get_device2 return nil if no driver is configure with the correct protocol

libraries/AP_Scripting/lua_bindings.cpp

@@ -682,6 +682,12 @@ int lua_get_CAN_device(lua_State *L) {
         }
     }
 
+    if (!scripting->_CAN_dev->initialized()) {
+        // Driver not initialized, probably because there is no can driver set to scripting
+        // Return nil
+        return 0;
+    }
+
     new_ScriptingCANBuffer(L);
     *((ScriptingCANBuffer**)luaL_checkudata(L, -1, "ScriptingCANBuffer")) = scripting->_CAN_dev->add_buffer(buffer_len);
 
@@ -707,6 +713,12 @@ int lua_get_CAN_device2(lua_State *L) {
         }
     }
 
+    if (!scripting->_CAN_dev2->initialized()) {
+        // Driver not initialized, probably because there is no can driver set to scripting 2
+        // Return nil
+        return 0;
+    }
+
     new_ScriptingCANBuffer(L);
     *((ScriptingCANBuffer**)luaL_checkudata(L, -1, "ScriptingCANBuffer")) = scripting->_CAN_dev2->add_buffer(buffer_len);