MM-30826: Sentry crash: nil deference in model.AuthorizeRequest (#16563)

The return statement after setting c.InvalidParam was missing

https://mattermost.atlassian.net/browse/MM-30826

```release-note
NONE
```

web/oauth.go

@@ -46,6 +46,7 @@ func authorizeOAuthApp(c *Context, w http.ResponseWriter, r *http.Request) {
 	authRequest := model.AuthorizeRequestFromJson(r.Body)
 	if authRequest == nil {
 		c.SetInvalidParam("authorize_request")
+		return
 	}
 
 	if err := authRequest.IsValid(); err != nil {