the rationale is that:
- the file name in IMAGEHLP_LINE* structures is returned as a pointer to
  an internal buffer
- in the W64 variant of APIs, two calls to fetch_buffer() are currently needed
  (one for first A allocation, second for W conversion)
- this generate bugs as it's assumed the two buffers are different

so the internal_line_t purpose is to factorize the implementations
of the 3 variants (A32, A64, W64) into a single code path
this insures a unique allocation, and at most, one conversion
Signed-off-by: Eric Pouech <eric.pouech@gmail.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>