Commit the actual fix for GH-17951

Sorry, my (ilutov's) bad. I reverted the change to verify the test, but forgot
to undo before pushing.

(cherry picked from commit 9b752a3)

Author: manuelm

main/main.c

@@ -346,7 +346,7 @@ static PHP_INI_MH(OnChangeMemoryLimit)
 		}
 
 		zend_ini_entry *max_mem_limit_ini = zend_hash_str_find_ptr(EG(ini_directives), ZEND_STRL("max_memory_limit"));
-		entry->value = zend_string_copy(max_mem_limit_ini->value);
+		entry->value = zend_string_init(ZSTR_VAL(max_mem_limit_ini->value), ZSTR_LEN(max_mem_limit_ini->value), true);
 		PG(memory_limit) = PG(max_memory_limit);
 
 		return SUCCESS;