CLEANUP: compression: do not test for buffer before calling b_alloc()

Now we know the function is idempotent, we don't need to run the
preliminary test anymore.
diff --git a/src/compression.c b/src/compression.c
index 26dcd42..da6213e 100644
--- a/src/compression.c
+++ b/src/compression.c
@@ -294,11 +294,8 @@
 		 * data and need a buffer now. We reuse the same buffer, as it's
 		 * not used out of the scope of a series of add_data()*, end().
 		 */
-		if (unlikely(!tmpbuf.size)) {
-			/* this is the first time we need the compression buffer */
-			if (b_alloc(&tmpbuf) == NULL)
-				return -1; /* no memory */
-		}
+		if (b_alloc(&tmpbuf) == NULL)
+			return -1; /* no memory */
 		b_reset(&tmpbuf);
 		memcpy(b_tail(&tmpbuf), comp_ctx->direct_ptr, comp_ctx->direct_len);
 		b_add(&tmpbuf, comp_ctx->direct_len);
diff --git a/src/flt_http_comp.c b/src/flt_http_comp.c
index de61cac..c9eb16b 100644
--- a/src/flt_http_comp.c
+++ b/src/flt_http_comp.c
@@ -66,9 +66,9 @@
 static int
 comp_flt_init_per_thread(struct proxy *px, struct flt_conf *fconf)
 {
-	if (!tmpbuf.size && b_alloc(&tmpbuf) == NULL)
+	if (b_alloc(&tmpbuf) == NULL)
 		return -1;
-	if (!zbuf.size && b_alloc(&zbuf) == NULL)
+	if (b_alloc(&zbuf) == NULL)
 		return -1;
 	return 0;
 }