Don't assign _largeByteBuffer until clear it will be used.
Don't assign _largeByteBuffer until clear it will be used.

BsonBinaryWriter._largeByteBuffer is lazily-allocated, but a path
following the allocation doesn't use it. Move the allocation into the
path that makes use of it, to avoid the null-check and potentially the
allocation.

ze-pequeno/Newtonsoft.Json,TylerBrinkley/Newtonsoft.Json,brjohnstmsft/Newtonsoft.Json,JamesNK/Newtonsoft.Json,jkorell/Newtonsoft.Json,ValtoLibraries/Newtonsoft.Json,PKRoma/Newtonsoft.Json,benaadams/Newtonsoft.Json,bfriesen/Newtonsoft.Json,skarllot/Newtonsoft.Json,oxwanawxo/Newtonsoft.Json