fluidsynth -- Use after free when using DLS files

The fluidsynth authors report:

A race condition during unloading of a DLS file can trigger a heap-based use-after-free. A concurrently running thread may be pending to unload a DLS file, leading to use of freed memory, if the synthesizer is being concurrently destroyed, or samples of the (unloaded) DLS file are concurrently used to synthesize audio. Realistically, both scenarios will result in a denial of service. In worst cases, it may result in arbitrary code execution in the context of an application using FluidSynth.

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