IsTailPaddedMemberArray uses a FieldDecl's

getTypeSourceInfo() without checking for NULL.
FieldDecls may have NULL TypeSourceInfo, and in
fact some FieldDecls generated by Clang -- and
all FieldDecls generated by LLDB -- have no
TypeSourceInfo.

This patch makes IsTailPaddedMemberArray check
for NULL.

llvm-svn: 156186