fix(win): accept minimal PDB70 CodeView records

[jpnurmi]

Validate the serialized record length instead of the padded C++ struct size so records with an empty PDB filename are accepted.

Tested by:

• fix(crashpad): preserve UUIDs from minimal PDB70 records sentry-native#2003

Original issue:

• crashpad discards the CodeView record of every MinGW/lld module, so minidumps carry no debug id sentry-native#2002

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