Changed "!fp" to "fp == NULL"

Change-Id: Ie19c4b19fda605b210db36128203d0db4726e5be
diff --git a/src/forward.c b/src/forward.c
index 7d647fd..e7e0d33 100644
--- a/src/forward.c
+++ b/src/forward.c
@@ -1311,7 +1311,7 @@
 		{
 		  FILE *fp;
 		  fp = fopen("/tmp/dns_query_log.txt", "a");
-		  if (!fp)
+		  if (fp == NULL)
 			{
 			  my_syslog(LOG_ERR, "failed to open /tmp/dns_query_log.txt: %s", strerror(errno));
 			}