Add const to methods that do not modify the object for which it is called

src/dbwrapper.cpp

@@ -184,7 +184,7 @@ bool CDBWrapper::IsEmpty()
 }
 
 CDBIterator::~CDBIterator() { delete piter; }
-bool CDBIterator::Valid() { return piter->Valid(); }
+bool CDBIterator::Valid() const { return piter->Valid(); }
 void CDBIterator::SeekToFirst() { piter->SeekToFirst(); }
 void CDBIterator::Next() { piter->Next(); }