fix invalid memory access in chart tests

Change-Id: I056101d146c939ff958c83efc57fd110e8d52509
fix incorrect ScAnnotationsObj UNO API, fdo#80551

The used index was a sheet local index but the returned position was
from a global container.

Change-Id: I0b9e9e7e9618c72daf8e6417bca9d3a1cb23abb1