Preserve errno if opening log file fails

src/logging.c

@@ -192,9 +192,11 @@ struct uc_log_destination *uc_log_new_file(const char *filename, int log_level,
 
     f = fopen(filename, "a"); 
     if (f == NULL) {
+       int saved_errno = errno; 
        free(dest->module_settings);
        free(name);
        free(dest);
+       errno = saved_errno;
        return NULL;
     }