Fix some tests in asan builds

Summary: zend-url.cpp was reading past the end of a string without verifying
its length. The other two tests were overflowing the VM stack, since it's
smaller for valgrind and asan. The new, smaller versions of the tests should be
just as useful. There are still a few more issues relating to C++ stack size
but I don't have time to get those right now.

Reviewed By: @edwinsmith

Differential Revision: D1566405