PR c++/71184: Fix NULL dereference in cp_parser_operator

PR c++/71184: Fix NULL dereference in cp_parser_operator

The source-range handling for the array form of operator
new/delete erroneously assumed that the "]" was present,
leading to a dereference of NULL when it's absent.

Fix it thusly.

gcc/cp/ChangeLog:
	PR c++/71184
	* parser.c (cp_parser_operator): For array new/delete, check that
	cp_parser_require returned a non-NULL token before dereferencing
	it.

gcc/testsuite/ChangeLog:
	PR c++/71184
	* g++.dg/pr71184.C: New test case.

From-SVN: r236483