Fix incorrect formatting when no symbol name is available.

Author: ZeroIntensity

Python/traceback.c

@@ -1221,9 +1221,8 @@ _Py_backtrace_symbols_fd(int fd, void *const *array, Py_ssize_t size)
 
         if (info[i].dli_sname == NULL
             && info[i].dli_saddr == 0) {
-            dprintf(fd, "  Binary file \"%s\", at %s [%p]\n",
-                    info[i].dli_fname ?: "",
-                    info[i].dli_sname ?: "",
+            dprintf(fd, "  Binary file \"%s\" [%p]\n",
+                    info[i].dli_fname ?: "<unknown>",
                     array[i]);
         }
         else {