Adding error string to list commands

Client-Server Protocol.md

@@ -128,7 +128,8 @@ Server:
 	"command": "list",
 	"accept": bool,
 	"items": int,
-	"chunks": int
+	"chunks": int,
+	"error": string
 }
 ```
 
@@ -147,7 +148,8 @@ Server:
 	"command": "getlist",
 	"remaining": int,
 	"cancel": bool,
-	"names": string[]
+	"names": string[],
+	"error": string
 }
 ```
 The client has to request every chunk until all names have been sent and `remaining` hits `0`.