Pacify GCC 16.1 -Wanalyzer-use-of-uninitialized-value

This fixes a false positive with gcc 16.1.1 20260501 (Red Hat
16.1.1-1) on x86-64.
* src/extract.c (set_stat): Use differently-worded but equivalent test
to help the compiler see that ts[0].tv_sec is used only if sedt.

src/extract.c

@@ -455,7 +455,7 @@ set_stat (char const *file_name,
 	}
       if (r == 0)
 	{
-	  if (incremental_option)
+	  if (ts[0].tv_nsec != UTIME_OMIT)
 	    check_time (file_name, ts[0]);
 	  check_time (file_name, ts[1]);
 	}