Fix mingw gcc 10.3 compiler warnings
The commits from this mr fixes build errors when building with -Werror were encountered with the mingw gcc compiler version 10.3 at !192 (merged).
The commits included are the result of a review performed on the mentioned merge request and outstanding issues are:
Depends on !192 (merged) to see the warnings and !286 (merged)
Fixes #383 (closed)
Edited by Ralf Habacker