PR libstdc++/63497
	include/bits/regex_executor.tcc (_Executor::_M_dfs,
	_Executor::_M_word_boundary): Avoid dereferecing _M_current at _M_end
	or other invalid position.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/branches/gcc-4_9-branch@218138 138bc75d-0d04-0410-961f-82ee72b054a4