Add more missing tests for getAccessibleContext returning NULL

--- a/wrapper/org/GNOME/Accessibility/AtkTable.java
+++ b/wrapper/org/GNOME/Accessibility/AtkTable.java
@@ -100,7 +100,10 @@ public class AtkTable {
 			acc_table.getAccessibleColumnDescription(column);
 
 		if (accessible != null) {
-			return accessible.getAccessibleContext().getAccessibleDescription();
+			AccessibleContext ac = accessible.getAccessibleContext();
+			if (ac != null) {
+				return ac.getAccessibleDescription();
+			}
 		}
 
 		return "";
@@ -124,7 +127,10 @@ public class AtkTable {
 			acc_table.getAccessibleRowDescription(row);
 
 		if (accessible != null) {
-			return accessible.getAccessibleContext().getAccessibleDescription();
+			AccessibleContext ac = accessible.getAccessibleContext();
+			if (ac != null) {
+				return ac.getAccessibleDescription();
+			}
 		}
 
 		return "";
--- a/wrapper/org/GNOME/Accessibility/AtkWrapper.java.in
+++ b/wrapper/org/GNOME/Accessibility/AtkWrapper.java.in
@@ -581,7 +581,10 @@ public class AtkWrapper {
         javax.accessibility.AccessibleRole role = ac.getAccessibleRole();
         javax.accessibility.AccessibleRole parent_role = null;
         if (parent != null) {
-          parent_role = parent.getAccessibleContext().getAccessibleRole();
+          AccessibleContext parent_ac = parent.getAccessibleContext();
+	  if (parent_ac != null) {
+	    parent_role = parent_ac.getAccessibleRole();
+	  }
         }
         if (role != null) {
           if (newValue == javax.accessibility.AccessibleState.FOCUSED ||
