[hotfix] Fix syntax error in Module\Register

- Prevents registration
- Addresses https://github.com/friendica/friendica/issues/7675#issuecomment-552070076

src/Module/Register.php

@@ -262,7 +262,7 @@ class Register extends BaseModule
 				$a->internalRedirect('register/');
 			}
 			// Is there text in the tar pit?
-			if (!empty($_POST('registertarpit'))) {
+			if (!empty($_POST['registertarpit'])) {
 				\notice(L10n::t('You have entered too much information.'));
 				$a->internalRedirect('register/');
 			}