Initialize appended/inserted Column backing arrays

When appending or inserting a new column into a table, the backing
arrays for those columns will now be initialized. This prevents null
pointer exceptions when attempting to modify appended or inserted
columns.

Author: awalter17

src/main/java/net/imagej/table/AbstractTable.java

@@ -143,6 +143,8 @@ public ArrayList<C> insertColumns(final int col, final int count) {
 		final ArrayList<C> result = new ArrayList<>(count);
 		for (int c = 0; c < count; c++) {
 			final C column = createColumn(null);
+			// initialize array
+			column.setSize(getRowCount());
 			result.add(column);
 			set(col + c, column);
 		}