This commit resets the Table::itemHeight to -1 on DPI change to make
sure that TableItem's height is still managed by the OS as it can be
changed by CDDS_SUBITEMPREPAINT callback and once it is changed to some
value, it will always remain the same and not recalculated by the OS
leading to inconsistent behaviour on different zooms.

contributes to
https://github.com/eclipse-platform/eclipse.platform.swt/issues/62 and
https://github.com/eclipse-platform/eclipse.platform.swt/issues/127