[lldb/DWARF] Fix a crash parsing invalid dwarf (pr49678)

If the debug info is missing the terminating null die, we would crash
when trying to access the nonexisting children/siblings. This was
discovered because the test case for D98619 accidentaly produced such
input.

GitOrigin-RevId: 2ecf928153fc56dcb6bb0bd910584eac86bc23bd
2 files changed