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

folly/FBVector.h

@@ -113,7 +113,7 @@ class fbvector {
     // note that 'allocate' and 'deallocate' are inherited from Allocator
     T* D_allocate(size_type n) {
       if (usingStdAllocator::value) {
-        return static_cast<T*>(malloc(n * sizeof(T)));
+        return static_cast<T*>(checkedMalloc(n * sizeof(T)));
       } else {
         return std::allocator_traits<Allocator>::allocate(*this, n);
       }