CLEANUP: Stop checking the pointer before calling `ring_free()`

Changes performed with this Coccinelle patch:

    @@
    expression e;
    @@

    - if (e != NULL) {
    	ring_free(e);
    - }

    @@
    expression e;
    @@

    - if (e) {
    	ring_free(e);
    - }

    @@
    expression e;
    @@

    - if (e)
    	ring_free(e);

    @@
    expression e;
    @@

    - if (e != NULL)
    	ring_free(e);
diff --git a/src/dns.c b/src/dns.c
index 8855f37..e5ddee7 100644
--- a/src/dns.c
+++ b/src/dns.c
@@ -421,8 +421,7 @@
 	}
 	return 0;
 out:
-	if (dgram->ring_req)
-		ring_free(dgram->ring_req);
+	ring_free(dgram->ring_req);
 
 	free(dgram);
 
diff --git a/src/resolvers.c b/src/resolvers.c
index ee70e45..4b2e03e 100644
--- a/src/resolvers.c
+++ b/src/resolvers.c
@@ -2484,13 +2484,11 @@
 				fd_delete(ns->dgram->conn.t.sock.fd);
 				close(ns->dgram->conn.t.sock.fd);
 			}
-			if (ns->dgram->ring_req)
-				ring_free(ns->dgram->ring_req);
+			ring_free(ns->dgram->ring_req);
 			free(ns->dgram);
 		}
 		if (ns->stream) {
-			if (ns->stream->ring_req)
-				ring_free(ns->stream->ring_req);
+			ring_free(ns->stream->ring_req);
 			task_destroy(ns->stream->task_req);
 			task_destroy(ns->stream->task_rsp);
 			free(ns->stream);
diff --git a/src/sink.c b/src/sink.c
index 55b6ad1..af0e891 100644
--- a/src/sink.c
+++ b/src/sink.c
@@ -1164,8 +1164,7 @@
 		free(sft);
 
 	if (sink) {
-		if (sink->ctx.ring)
-			ring_free(sink->ctx.ring);
+		ring_free(sink->ctx.ring);
 
 		LIST_DELETE(&sink->sink_list);
 		free(sink->name);