libvips: libvips: Denial of Service via Malformed PFM Image Processing

libvips 8.19.0 contains a memory access vulnerability when processing little-endian PFM images. If the PFM text header length is not a multiple of four bytes, the mmap-based loader can expose pixel data at an address that is not properly aligned for float access. vips_avg_scan() subsequently dereferences the buffer through a float pointer, resulting in undefined behavior and process termination on strict-alignment architectures or UBSan-instrumented builds, leading to denial of service.