Fix normalize_path's handling of "/.."

Currently it normalizes the path to a string with a single uninitialized
byte. It should instead normalize it to "/".

Bug: none
Test: /data/nativetest/linker-unit-tests/linker-unit-tests32
Test: /data/nativetest64/linker-unit-tests/linker-unit-tests64
Change-Id: I06e0f7598d16acfa21875dad53efbc293cfeb44d