Pass msg object where possible

As described on https://nodered.org/docs/user-guide/writing-functions#handling-errors

src/matrix-send-file.js

@@ -32,7 +32,7 @@ module.exports = function(RED) {
             }
 
             if(!node.server.isConnected()) {
-                node.error("Matrix server connection is currently closed", {});
+                node.error("Matrix server connection is currently closed", msg);
                 node.send([null, msg]);
             }
 
@@ -58,7 +58,7 @@ module.exports = function(RED) {
             }
 
             if(!msg.payload) {
-                node.error('msg.payload is required', {});
+                node.error('msg.payload is required', msg);
                 return;
             }