[Object][MachO] Handle end iterator in getSymbolType()

Fix a bug in MachOObjectFile::getSymbolType() that it is not checking if
the iterator is end() before deference the iterator. Instead, return
`Other` type, which aligns with the behavior of `llvm-nm`.

rdar://75291638

Reviewed By: davide, ab

Differential Revision: https://reviews.llvm.org/D98739