fix: reset printToPDF queue after a rejection
The module-scoped `pendingPromise` in `webContents.printToPDF` was chained
with `.then(onFulfilled)` and never cleared. Once a call rejected (e.g.
an out-of-range `pageRanges` like `"999"`), subsequent calls chained onto
the rejected promise and short-circuited without ever invoking
`_printToPDF` — so every following call re-surfaced the original error.
Replace the shared variable with a per-`WebContents` `WeakMap` queue that
swallows prior rejections before chaining and clears its entry once the
tail drains.
89050762c6