Fix SubList implementation in extensions

Author: Snipx

itext/itext.io/itext/io/IOExtensions.cs

@@ -47,6 +47,7 @@ source product.
 using System.IO;
 using System.Reflection;
 using System.Text;
+using iText.IO.Util.Collections;
 
 namespace iText.IO {
     internal static class IOExtensions {
@@ -98,6 +99,13 @@ public static long Skip(this Stream s, long n) {
         }
 
         public static List<T> SubList<T>(this IList<T> list, int fromIndex, int toIndex) {
+            if (list is SingletonList<T>) {
+                if (fromIndex == 0 && toIndex >= 1) {
+                    return new List<T>(list);
+                } else {
+                    return new List<T>();
+                }
+            }
             return ((List<T>) list).GetRange(fromIndex, toIndex - fromIndex);
         }
 

itext/itext.kernel/KernelExtensions.cs

@@ -113,9 +113,17 @@ public static long Skip(this Stream s, long n) {
         return n;
     }
 
-    public static List<T> SubList<T>(this IList<T> list, int fromIndex, int toIndex) {
-        return ((List<T>) list).GetRange(fromIndex, toIndex - fromIndex);
-    }
+	public static List<T> SubList<T>(this IList<T> list, int fromIndex, int toIndex) {
+		if (list is SingletonList<T>) {
+			if (fromIndex == 0 && toIndex >= 1) {
+				return new List<T>(list);
+			} else {
+				return new List<T>();
+			}
+		}
+		return ((List<T>) list).GetRange(fromIndex, toIndex - fromIndex);
+	}
+
 
     public static void AddAll<T>(this IList<T> list, IEnumerable<T> c) {
         ((List<T>) list).AddRange(c);

itext/itext.layout/itext/layout/LayoutExtensions.cs

@@ -172,9 +172,16 @@ public static TValue Put<TKey, TValue>(this IDictionary<TKey, TValue> col, TKey
             return oldVal;
         }
 
-        public static List<T> SubList<T>(this IList<T> list, int fromIndex, int toIndex) {
-            return ((List<T>) list).GetRange(fromIndex, toIndex - fromIndex);
-        }
+		public static List<T> SubList<T>(this IList<T> list, int fromIndex, int toIndex) {
+			if (list is SingletonList<T>) {
+				if (fromIndex == 0 && toIndex >= 1) {
+					return new List<T>(list);
+				} else {
+					return new List<T>();
+				}
+			}
+			return ((List<T>) list).GetRange(fromIndex, toIndex - fromIndex);
+		}
 
         public static String[] Split(this String str, String regex) {
             return str.Split(regex.ToCharArray());