Fix bidi purge loop logic a bit

Otherwise you could skip one element by accident. This does not have
direct consequences, but may lead to slightly wrong behaviour when
there are stray opening brackets.

Signed-off-by: Laslo Hunhold <dev@frign.de>
diff --git a/src/bidirectional.c b/src/bidirectional.c
index 90aa423..c4a5057 100644
--- a/src/bidirectional.c
+++ b/src/bidirectional.c
@@ -636,8 +636,9 @@
 
 					/* remove all uncompleted FIFO elements
 					 * above i - 1 */
-					for (j = i; j < fifo_len; j++) {
+					for (j = i; j < fifo_len;) {
 						if (fifo[j].complete) {
+							j++;
 							continue;
 						}