[C++][GPU] IPC writer attempts to read non-CPU memory when it needs to shift offsets

[pitrou]

Describe the bug, including details regarding any error messages, version, and platform.

As found out in PR #46706, when the IPC writer encounters an offsets buffer starting with a non-zero offset, it produces a shifted version of the offsets by reading directly from the original buffer. This does not work if the buffer is a non-CPU buffer.

Component(s)

C++, GPU