[SEDONA-401] Handle null values in RS_AsMatrix

[iGN5117]

Did you read the Contributor Guide?

• Yes, I have read Contributor Rules and Contributor Development Guide

Is this PR related to a JIRA ticket?

• Yes, the URL of the associated JIRA ticket is https://issues.apache.org/jira/browse/SEDONA-401. The PR name follows the format [SEDONA-XXX] my subject.

What changes were proposed in this PR?

• Fix bugs in RS_AsMatrix to handle null values

How was this patch tested?

• Tested asMatrix with a raster having null values

Did this PR include necessary documentation updates?

• No, this PR does not affect any public API so no need to change the docs.