[Win32] Release DPI change callback also on failure - #3563
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The processing of a zoom change can be scheduled asynchronously via a native timer, for which a callback is allocated and released again once the processing has been performed. If the processing fails, the callback is currently not released. Callback slots are a limited resource shared by the whole application. Once they are exhausted, allocating a callback fails, which makes the scheduling of the zoom change processing fall back to performing it synchronously and can break other functionality relying on callbacks as well. The callback is therefore released independently of the outcome of the processing. Assisted-by: Claude Opus 5 <noreply@anthropic.com>
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When a zoom change is processed asynchronously, a native callback is allocated for the timer triggering the processing and is released again once the processing has been performed. If the processing fails, the callback is never released.
Callback slots are a limited resource shared by the whole application, so repeatedly failing zoom change processing eventually exhausts them. From then on, allocating a callback fails, which makes the scheduling of the zoom change processing silently fall back to performing it synchronously and can break unrelated functionality relying on callbacks as well.
The callback is now released independently of the outcome of the processing. There is no automated test for this, as the leak is only observable by exhausting the application-wide callback pool, which cannot be provoked in a test without affecting everything else running in the same process. The change has no effect on the successful case, in which the callback was already released.
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