Migrate all the api4 to handle errors in idiomatic way (#9143)

api4/command.go

@@ -202,7 +202,9 @@ func executeCommand(c *Context, w http.ResponseWriter, r *http.Request) {
 	if err != nil {
 		c.Err = err
 		return
-	} else if channel.Type != model.CHANNEL_DIRECT && channel.Type != model.CHANNEL_GROUP {
+	}
+
+	if channel.Type != model.CHANNEL_DIRECT && channel.Type != model.CHANNEL_GROUP {
 		// if this isn't a DM or GM, the team id is implicitly taken from the channel so that slash commands created on
 		// some other team can't be run against this one
 		commandArgs.TeamId = channel.TeamId