update to libgit2 v1.4.3

[chcg]

• updated to libgit2 from tag https://github.com/libgit2/libgit2/releases/tag/v1.4.3
• build by https://ci.appveyor.com/project/chcg/libgit2/builds/4387525…2 based on https://github.com/chcg/libgit2/tree/Appveyor_v1.4.3 for PlatformToolset=v141
• not tested for compatibility

[pnedev]

Hi Christian, Thank you very much for your both merge requests, they are of great help! :+1: BR