[SYSTEMDS-3898] Fix robustness quantile/iqr with averaging

This patch fixes the quantile value-pick kernel for the case with
averaging which ran into out-of-bounds exceptions for instances of
outlierByIQR because the kernel was not robust against quantiles at
extreme boundaries values.

Author: mboehm7

src/main/java/org/apache/sysds/runtime/matrix/data/MatrixBlock.java

@@ -4804,7 +4804,7 @@ public double pickValue(double quantile, boolean average) {
 
 		if ( get(i,1) != 0 ) {
 			// i^th value is present in the data set, simply return it
-			if ( average ) {
+			if ( average && pos < getNumRows()-1 ) {
 				if(pos < t) {
 					return get(i,0);
 				}