Log Message:
cad/libredwg: Update to 0.12.3

LibreDWG version 0.12.3 - 2021/02/26 - beta:

Minor bugfixes:
  * Fixed many more minor fuzzer errors, detected with the new llvmfuzz.
  * Harmonize UBSAN access for unaligned shorts (unicode strings).
    Wrong only with UBSAN or HAVE_ALIGNED_ACCESS_REQUIRED.
  * Fix dwg2dxf/dxf2dwg uppercase extension problem (Windows) (GH #311).
  * Fix section_string_stream offset for r2010 beta 2 (many public samples) (GH #318)
Minor features:
  * Added google oss-fuzz integration, by David Korczynski (PR #316)
    libredwg is now fuzzed twice daily.
  * Added examples/llvmfuzz for libfuzzer and the google oss-fuzz service.