Solaris fix for VRT_error

If VRT_error is called with reason==NULL, WSL() will eventually call
strlen(0), which will cause a SIGSEGV on (Open)Solaris.  Fix this by
checking if the reason is empty and just use (null) in that case.

Fixes: 458


git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@3847 d4fa192b-c00b-0410-8231-f00ffab90ce4

bin/varnishd/cache_vrt.c

@@ -62,7 +62,8 @@ VRT_error(struct sess *sp, unsigned code, const char *reason)
 {
 
 	CHECK_OBJ_NOTNULL(sp, SESS_MAGIC);
-	WSL(sp->wrk, SLT_Debug, 0, "VCL_error(%u, %s)", code, reason);
+	WSL(sp->wrk, SLT_Debug, 0, "VCL_error(%u, %s)", code, reason ? 
+	    reason : "(null)");
 	sp->err_code = code ? code : 503;
 	sp->err_reason = reason ? reason : http_StatusMessage(sp->err_code);
 }