So far, the test case was also testing the offset -1. This test cases
failed if the string is immediately at the beginning of the memory
region, though, and the offset -1 hence belonged to a different memory
region.
The fix is rather straightforward:
Passing an offset of -1 is not used by any actual clients of lldb-dap,
anyway. As such, this commit simply removes the corresponding test case.
620738e662