Changes related to following tracker items:

[2025916] ODBC binds empty string as null?
[2000408] DynamicAny non-initialized state support
[1981130] pointless comparison of unsigned integer with zero

and some refactoring.

Warning: only tested on Windows.

Data/src/MetaColumn.cpp

@@ -59,7 +59,6 @@ MetaColumn::MetaColumn(std::size_t position,
 	_type(type),
 	_nullable(nullable)
 {
-	poco_assert(position >= 0);
 }