Fix permission logic

doc/config.md

@@ -160,6 +160,6 @@ Description: This sets the group of a user.
 > `UserGroups[k]`
 ```
 Type: string
-Default: ""
+Default: "default"
 Description: The group of the user.
 ```

perms.go

@@ -7,7 +7,11 @@ func (cc *ClientConn) Perms() []string {
 		return []string{}
 	}
 
-	grp := Conf().UserGroups[cc.name]
+	grp, ok := Conf().UserGroups[cc.name]
+	if !ok {
+		grp = "default"
+	}
+
 	if perms, ok := Conf().Groups[grp]; ok {
 		return perms
 	}