Fix crashes when binding or reading blob values

[simolus3]

This fixes two issues:

1. When binding a JS ArrayBuffer as a blob value, we used to pass the underlying data pointer of the buffer to the shared_ptr constructor. This makes the value take ownership of the underlying contents, which is not correct! The JS engine keeps ownership of data, we should clone instead. Binding the buffer causes a duplicate free when the JS engine eventually collects garbage, crashing the app.
2. When reading SQLITE_BLOB values, memcpy was called on an uninitialized uint8_t *. Writing into the uninitialized pointer is undefined behavior (crashing the app is a best-case scenario here).