Fix warnings about unused return values

Change-Id: I9682c6b5a0bba400050e91fe89b2883f7bb6465f
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/lua/luaplugin.cpp

@@ -165,7 +165,7 @@ public:
         m_readCallback = {};
 
         QFile f(":/lua/scripts/ilua.lua");
-        f.open(QIODevice::ReadOnly);
+        QTC_CHECK(f.open(QIODevice::ReadOnly));
         const auto ilua = QString::fromUtf8(f.readAll());
         m_luaState = runScript(ilua, "ilua.lua", [this](sol::state &lua) {
             lua["print"] = [this](sol::variadic_args va) {