MemoryMappedView leak #133744

A few more findings from the same 64KiB-page machine, separate from the thunk and GC bitmap-accounting issues above:

2. Empty memory-mapped views leak one OS-page mapping on Unix. CreateView maps one byte for an empty view but records a native length of zero. Disposal then calls munmap(address, 0), which fails. Reproduced against the locally built libraries: all 32 disposed empty views remained mapped. This isn't exclusive to 64KiB pages, but the leaked virtual mapping is 64KiB per view here, rather than 4KiB.

Originally posted by @EgorBo in #133675