Memory corruption via overflowing FFT allocation size

Heap buffer overflow in KISS FFT before 1b083165 allows local users to corrupt process memory through an oversized FFT length on 32-bit systems. kiss_fft_alloc() multiplies the caller-controlled nfft value while calculating its allocation size without first rejecting values that overflow size_t, so malloc() returns an undersized buffer and the twiddle-factor loop writes beyond it. The condition requires a 32-bit build and a calling application that passes an extremely large FFT length; the resulting write corrupts memory and can crash the process.