Fix IOBuf::createCombined()

Summary:
IOBuf::createCombined was derefencing a nullptr in case of allocation failure.
This patches fixes this issue by throwing std::bad_alloc if malloc() returns a
nullptr.

Reviewed By: yfeldblum

Differential Revision: D9763331

fbshipit-source-id: 7d9b9265079e74f5c63c8c8809099de97342f54d

folly/io/IOBuf.cpp

@@ -245,7 +245,7 @@ unique_ptr<IOBuf> IOBuf::createCombined(std::size_t capacity) {
   // SharedInfo struct, and the data itself all with a single call to malloc().
   size_t requiredStorage = offsetof(HeapFullStorage, align) + capacity;
   size_t mallocSize = goodMallocSize(requiredStorage);
-  auto* storage = static_cast<HeapFullStorage*>(malloc(mallocSize));
+  auto* storage = static_cast<HeapFullStorage*>(checkedMalloc(mallocSize));
 
   new (&storage->hs.prefix) HeapPrefix(kIOBufInUse | kDataInUse);
   new (&storage->shared) SharedInfo(freeInternalBuf, storage);