fix(DomRenderer): resilience when buffer lines are missing (#5998)

* fix(DomRenderer): skip missing buffer lines during row render

renderRows and link underline refresh stopped updating when any
viewport row lacked buffer data, leaving stale DOM on rows below.
Match ImageStorage.render behavior: clear the row element when
present and continue with remaining rows.

Co-authored-by: Cursor <cursoragent@cursor.com>

* fix(DomRenderer): clear blink state when skipping missing lines

When a viewport row has no buffer line, renderRows clears the row DOM
and continues but did not reset _rowHasBlinkingCells for that row.
That could leave the text blink manager thinking blinking cells remain
after the row was emptied.

Clear blink state for the row when skipping a missing buffer line,
including during link underline refresh.

Co-authored-by: Cursor <cursoragent@cursor.com>

---------

Co-authored-by: Cursor <cursoragent@cursor.com>

src/browser/renderer/dom/DomRenderer.ts

@@ -536,9 +536,14 @@ export class DomRenderer extends Disposable implements IRenderer {
     for (let y = start; y <= end; y++) {
       const row = y + buffer.ydisp;
       const rowElement = this._rowElements[y];
+      if (!rowElement) {
+        continue;
+      }
       const lineData = buffer.lines.get(row);
-      if (!rowElement || !lineData) {
-        break;
+      if (!lineData) {
+        rowElement.replaceChildren();
+        this._setRowBlinkState(y, false);
+        continue;
       }
       rowElement.replaceChildren(
         ...this._rowFactory.createRow(
@@ -610,9 +615,14 @@ export class DomRenderer extends Disposable implements IRenderer {
     for (let i = y; i <= y2; ++i) {
       const row = i + buffer.ydisp;
       const rowElement = this._rowElements[i];
+      if (!rowElement) {
+        continue;
+      }
       const bufferline = buffer.lines.get(row);
-      if (!rowElement || !bufferline) {
-        break;
+      if (!bufferline) {
+        rowElement.replaceChildren();
+        this._setRowBlinkState(i, false);
+        continue;
       }
       rowElement.replaceChildren(
         ...this._rowFactory.createRow(