fix(addon-image): skip missing lines in viewportResize

viewportResize walks the full buffer when the terminal widens but
called line.getBg without checking that lines.get(row) returned a
line. During resize or trim gaps that could throw and abort tile
expansion for remaining rows.

Skip missing buffer lines with continue, consistent with render().

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

addons/addon-image/src/ImageStorage.ts

@@ -514,6 +514,9 @@ export class ImageStorage implements IDisposable {
     const oldCol = this._viewportMetrics.cols - 1;
     for (let row = 0; row < rows; ++row) {
       const line = buffer.lines.get(row) as IBufferLineExt;
+      if (!line) {
+        continue;
+      }
       if (line.getBg(oldCol) & BgFlags.HAS_EXTENDED) {
         const e: IExtendedAttrsImage = line._extendedAttrs[oldCol] ?? EMPTY_ATTRS;
         const imageId = e.imageId;