NVARCHAR(MAX) length for portableTableColumnDefiniton should not be divided

[MaximilianSpeer]

Bug Report

When introspecting a schema from an SqlServer database a nvarchar(max) a TypeError is raised.
Apparently this happens because the length of an nvarchar is divided by two in the SQLServerSchemaManager::getPortableTableColunmnDefinition. As the MAX length is read as -1 this leads to a float length (-0.5).

This can be simply reproduced by introspecting a SqlServer database schema containing a nvarchar(max) column.