Clear heads for unmark operators in tag and match rules.

libwccl/ops/match/actions/unmarkmatch.cpp

@@ -33,6 +33,7 @@ void UnmarkMatch::execute(const ActionExecContext& context) const
 	for (int i = 0; i < channel.size(); ++i) {
 		if (channel.segments()[i] == segment_idx) {
 			channel.set_segment_at(i, 0);
+			channel.set_head_at(i, false);
 		}
 	}
 }

libwccl/ops/tagactions/unmark.cpp

@@ -37,6 +37,7 @@ Bool Unmark::execute(const ActionExecContext& context) const
 	for (int i = 0; i < channel.size(); ++i) {
 		if (channel.segments()[i] == segment_idx) {
 			channel.set_segment_at(i, 0);
+			channel.set_head_at(i, false);
 		}
 	}
 	return Bool(true);