fix: ignore empty spans

Author: pascalkuthe

helix-core/src/syntax/span.rs

@@ -76,6 +76,10 @@ impl SpanIter {
         use HighlightEvent::*;
 
         debug_assert!(span.start <= span.end);
+        if span.start == span.end {
+            return;
+        }
+
         self.event_queue
             .push_back(HighlightStart(Highlight(span.scope)));
         self.range_ends.push(span.end);