CLEANUP: sample: remove useless tests in fetch functions for l4 != NULL

The stream may never be null given that all these functions are called
from sample_process(). Let's remove this now confusing test which
sometimes happens after a dereference was already done.
diff --git a/src/payload.c b/src/payload.c
index 3a2dc15..9d7774c 100644
--- a/src/payload.c
+++ b/src/payload.c
@@ -48,9 +48,6 @@
 {
 	struct channel *chn;
 
-	if (!s)
-		return 0;
-
 	chn = ((opt & SMP_OPT_DIR) == SMP_OPT_DIR_RES) ? &s->res : &s->req;
 	if (!chn->buf)
 		return 0;
@@ -71,9 +68,6 @@
 	struct channel *chn;
 	const unsigned char *data;
 
-	if (!s)
-		goto not_ssl_hello;
-
 	chn = ((opt & SMP_OPT_DIR) == SMP_OPT_DIR_RES) ? &s->res : &s->req;
 	if (!chn->buf)
 		goto not_ssl_hello;
@@ -140,7 +134,7 @@
 	int version, bleft, msg_len;
 	const unsigned char *data;
 
-	if (!s || !s->req.buf)
+	if (!s->req.buf)
 		return 0;
 
 	msg_len = 0;
@@ -277,9 +271,6 @@
 	struct channel *chn;
 	unsigned char *data;
 
-	if (!s)
-		goto not_ssl_hello;
-
 	chn = ((opt & SMP_OPT_DIR) == SMP_OPT_DIR_RES) ? &s->res : &s->req;
 	if (!chn->buf)
 		goto not_ssl_hello;
@@ -415,7 +406,7 @@
 	int bleft;
 	const unsigned char *data;
 
-	if (!s || !s->req.buf)
+	if (!s->req.buf)
 		return 0;
 
 	smp->flags = SMP_F_CONST;
@@ -542,9 +533,6 @@
 	/* by default buf offset == len offset + len size */
 	/* buf offset could be absolute or relative to len offset + len size if prefixed by + or - */
 
-	if (!s)
-		return 0;
-
 	chn = ((opt & SMP_OPT_DIR) == SMP_OPT_DIR_RES) ? &s->res : &s->req;
 	if (!chn->buf)
 		return 0;
@@ -592,9 +580,6 @@
 	unsigned int buf_size = arg_p[1].data.uint;
 	struct channel *chn;
 
-	if (!s)
-		return 0;
-
 	chn = ((opt & SMP_OPT_DIR) == SMP_OPT_DIR_RES) ? &s->res : &s->req;
 	if (!chn->buf)
 		return 0;