KissFFT Integer Overflow Heap Buffer Overflow via kiss_fft_alloc

KissFFT versions prior to the fix commit 1b083165 contain an integer overflow in kiss_fft_alloc() in kiss_fft.c on platforms where size_t is 32-bit. The nfft parameter is not validated before being used in a size calculation (sizeof(kiss_fft_cpx) * (nfft - 1)), which can wrap to a small value when nfft is large. As a result, malloc() allocates an undersized buffer and the subsequent twiddle-factor initialization loop writes nfft elements, causing a heap buffer overflow. This vulnerability only affects 32-bit architectures.