We used to expect a fixed number of DBI substreams (the expected number depended on the DBI header version). Recent MSVC generate a different number as we expected. Implement a more flexible scheme where we allow any number of streams. This lets these recent PDB files to be properly displayed by winedump, and loaded/parsed by dbghelp.
-- v2: dbghelp: Don't expected a fixed number of substreams in DBI header (PDB). winedump: Don't expect a fixed number of substreams in DBI header (PDB).