qt,cpp: Consistently use nullptr and override

* lang/cpp/src/Makefile.am, lang/qt/src/Makefile.am (AM_CPPFLAGS):
Add suggest-override and zero-as-null-pointer-constant warnings.

* lang/cpp/src/*, lang/qt/src/*: Consistenly use nullptr and override.

--
This was especially important for the headers so that downstream
users of GpgME++ or QGpgME do not get flooded by warnings if
they have these warnings enabled.

It also improves compiler errors/warnings in case of accidental
mistakes.

1 files changed, 1 insertions, 1 deletions

diff --git a/lang/qt/src/qgpgmekeylistjob.cpp b/lang/qt/src/qgpgmekeylistjob.cpp
index 891b0bd7..295e612d 100644
--- a/lang/qt/src/qgpgmekeylistjob.cpp
+++ b/lang/qt/src/qgpgmekeylistjob.cpp
@@ -69,7 +69,7 @@ static KeyListResult do_list_keys(Context *ctx, const QStringList &pats, std::ve
     const _detail::PatternConverter pc(pats);
 
     if (const Error err = ctx->startKeyListing(pc.patterns(), secretOnly)) {
-        return KeyListResult(0, err);
+        return KeyListResult(nullptr, err);
     }
 
     Error err;