unregister INI entries and fix invalid read on shutdown (#8042)

php/ext/google/protobuf/protobuf.c

@@ -297,6 +297,7 @@ static PHP_MINIT_FUNCTION(protobuf) {
 }
 
 static PHP_MSHUTDOWN_FUNCTION(protobuf) {
+  UNREGISTER_INI_ENTRIES();
   return SUCCESS;
 }