StringConvertibleMatrixView may throw an exception if it is reused

[abeham]

This problem first appeared when changing a parameter of the PSO. To reproduce:

1. Open the PSO sample
2. Clear the value of the VelocityBounds parameter in the SwarmUpdater operator
3. Set a new value and choose DoubleMatrix

A workaround exists, if the view is switched to another parameter and then back to the VelociyBounds parameter the matrix can be set without error.

Explanation: The ViewHost caches the current view. So after clearing the old matrix, its view as well as the matrix are still present in memory, but the view is hidden. When a new matrix is created, the view is reused again. When the Content property is changed UpdateData is called and there the non-empty collection of columns of this view are cleared. This triggers a cell validating event. The event however is canceled as it does not address a valid cell (the new DoubleMatrix doesn't have rows or columns). When UpdateData continues to clear the rows the datagridview complains that there are cells that are not comitted.

[mkommend]

r15074: Changed StringConvertibleMatrixView to avoid CellValidating events of not existing cells.

[abeham]

Reviewed r15074: ok.