[scudo] Fix bad request handling when allocator has not been initialized

Summary:
In a few functions (`scudoMemalign` and the like), we would call
`ScudoAllocator::FailureHandler::OnBadRequest` if the parameters didn't check
out. The issue is that if the allocator had not been initialized (eg: if this
is the first heap related function called), we would use variables like
`allocator_may_return_null` and `exitcode` that still had their default value
(as opposed to the one set by the user or the initialization path).

To solve this, we introduce `handleBadRequest` that will call `initThreadMaybe`,
allowing the options to be correctly initialized.

Unfortunately, the tests were passing because `exitcode` was still 0, so the
results looked like success. Change those tests to do what they were supposed
to.

Reviewers: alekseyshl

Reviewed By: alekseyshl

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D37853

llvm-svn: 313294