Leave the RHS of a GrammarSymbolSet move default initialized

Previously the RHS was left as it was when, technically, it should be
restored to its default initialized state.  This fix exchanges the
RHS GrammarSymbolSet values with their default initialized values to
correct that error.

src/lalr/GrammarSymbolSet.cpp

@@ -28,8 +28,8 @@ GrammarSymbolSet::GrammarSymbolSet( size_t symbols )
 
 GrammarSymbolSet::GrammarSymbolSet( GrammarSymbolSet&& set )
 : set_( std::move(set.set_) )
-, minimum_(set.minimum_)
-, maximum_(set.maximum_)
+, minimum_( std::exchange(set.minimum_, numeric_limits<size_t>::max()) )
+, maximum_( std::exchange(set.maximum_, numeric_limits<size_t>::min()) )
 {
 }