MINOR: http-htx: Make 'internal.htx_blk_data' return a binary string

This internal sample fetch now returns a binary string (SMP_T_BIN) instead of a
character string.
diff --git a/src/http_htx.c b/src/http_htx.c
index b1940eb..6b1d11f 100644
--- a/src/http_htx.c
+++ b/src/http_htx.c
@@ -1261,7 +1261,7 @@
 
 		chunk_initlen(&smp->data.u.str, val.ptr, val.len, val.len);
 	}
-	smp->data.type = SMP_T_STR;
+	smp->data.type = SMP_T_BIN;
 	smp->flags = SMP_F_CONST | SMP_F_VOLATILE | SMP_F_MAY_CHANGE;
 	return 1;
 }