fix(PdfPageView): dispose the previous image before replacing it

[bschmalb-ksta]

Fixes #697.

_PdfPageViewState._updateImage overwrites _image without disposing the previous one, so every re-render that changes the requested page size (a zoom tier change, a layout change, a pageSizeCallback returning a new size) orphans a full-resolution decoded ui.Image. The only _image?.dispose() in the class is in _clearCache(), which this path never calls.

It also lacked a mounted guard on the assignment — the existing check only guarded setState. If the widget was disposed during the await, _clearCache() had already run and nulled _image, and the assignment then wrote a fresh image into a dead State where nothing would ever dispose it.

This is the second half of #110, which was closed as fixed in 1.0.51; only the dispose() half landed.

The fix matches what PdfViewer already does in pdf_viewer.dart (lines 1760-1764 and 1847-1852): guard on !mounted, dispose the old image, then swap.

final newImage = await pageImage.createImage();
pageImage.dispose();
if (!mounted) {
  newImage.dispose();
  return;
}
_image?.dispose();
_image = newImage;
setState(() {});

Kept deliberately minimal — no reformatting, no changelog entry (happy to add one if you'd like). I could not run dart analyze against the workspace locally: dependency resolution fails on meta (pdfium_flutter wants 1.17.0 via the Flutter SDK's flutter_test, pdfrx_engine wants ^1.18.0). That failure reproduces identically on unmodified master, so it is unrelated to this change.

[espresso3389]

This fix has been released in pdfrx 2.4.8.

Written by Codex