throw std::bad_alloc if memory can't be allocated (#888)
throw std::bad_alloc if memory can't be allocated (#888)

Summary:
Bug fix: call `reserve()` trying to allocate more memory than available
Pull Request resolved: https://github.com/facebook/folly/pull/888

Reviewed By: ot

Differential Revision: D9234444

Pulled By: yfeldblum

fbshipit-source-id: 4d12236aee745ad663d95a370d273f619f92b1bd

facebook/folly,facebook/folly,facebook/folly,facebook/folly,facebook/folly