Fix: Assertion failed: (!m_first_die || m_first_die == m_die_array.front()),...

Fix: Assertion failed: (!m_first_die || m_first_die == m_die_array.front()), function ExtractDIEsRWLocked

xbolva00 bugreported $subj in: https://reviews.llvm.org/D46810#1247410
It can happen only from the line:
	m_die_array.back().SetEmptyChildren(true);

In the case DW_TAG_compile_unit has DW_CHILDREN_yes but there is only 0 (end of
list, no children present). Therefore the assertion can fortunately happen only
with a hand-crafted DWARF or with DWARF from some suboptimal compilers.

Differential Revision: https://reviews.llvm.org/D53255

llvm-svn: 344605