Revert "Remove class validation. zend_lookup_class_ex() performs it anyway."

This reverts commit 61cf135.

Class name validation is only performed if key is not passed. Here, lc_name is passed as key.

Author: dstogov

ext/standard/var_unserializer.re

@@ -1171,6 +1171,12 @@ object ":" uiv ":" ["]	{
 			break;
 		}
 
+		if (!zend_is_valid_class_name(class_name)) {
+			zend_string_release_ex(lc_name, 0);
+			zend_string_release_ex(class_name, 0);
+			return 0;
+		}
+
 		/* Try to find class directly */
 		BG(serialize_lock)++;
 		ce = zend_lookup_class_ex(class_name, lc_name, 0);