read a bitmap from a serialized version. This is meant to be compatible with the Java and Go versions. See format specification at https://github.com/RoaringBitmap/RoaringFormatSpec
In case of failure, a null pointer is returned. This function is unsafe in the sense that if there is no valid serialized bitmap at the pointer, then many bytes could be read, possibly causing a buffer overflow. For a safer approach, call roaring_bitmap_portable_deserialize_safe.