[scudo][standalone] Fix for releaseToOS prior to init

Summary:
cferris@ found an issue where calling `releaseToOS` prior to any other
heap operation would lead to a crash, due to the allocator not being
properly initialized (it was discovered via `mallopt`).

The fix is to call `initThreadMaybe` prior to calling `releaseToOS` for
the Primary.

Add a test that crashes prior to fix.

Reviewers: hctim, cferris, pcc, eugenis

Subscribers: #sanitizers, llvm-commits

Tags: #sanitizers, #llvm

Differential Revision: https://reviews.llvm.org/D70552