Fix IDL compilation bugs

[mikebattista]

1. IDL files that don't have corresponding header files are being skipped over when converting MIDL attributes to SAL annotations
2. Only the first MIDL attribute list is being converted to SAL annotations

Discovered while investigating #1570. strmif.idl includes other idl files whose MIDL attributes weren't being converted to SAL annotations. A few other IDL files follow the same pattern.

While comparing the diff for 1, a handful of APIs lost attributes which appeared to be caused by a bug with how multiple MIDL attribute lists are handled.