Fix out of bound issue in ContextStack operation (#1288)

Author: NicolasDorier

NBitcoin.Tests/script_tests.cs

@@ -1012,6 +1012,20 @@ public void script_PushData()
 			AssertEx.StackEquals(pushdata4Stack.Stack, directStack.Stack);
 		}
 
+		[Fact]
+		[Trait("UnitTest", "UnitTest")]
+		public void script_OPNIP()
+		{
+			var context = new ScriptEvaluationContext()
+			{
+				ScriptVerify = ScriptVerify.P2SH
+			};
+			var directStack = context.Clone();
+			var direct = new Script(Encoders.Hex.DecodeData("000360670000005b770100000000005b770100000000000008777760779f00000877776077"));
+			var res = directStack.EvalScript(direct, new TransactionChecker(Network.CreateTransaction(), 0), HashVersion.Original);
+			Assert.True(res);
+		}
+
 		static Network Network => Network.Main;
 
 		[Fact]

NBitcoin/ScriptEvaluationContext.cs

@@ -2491,9 +2491,9 @@ public void Remove(int from)
 		public void Remove(int from, int to)
 		{
 			int toRemove = to - from;
-			for (int i = Count + from; i < Count + from + toRemove; i++)
+			for (int i = 0; i < toRemove; i++)
 			{
-				for (int y = Count + from; y < Count; y++)
+				for (int y = Count + from; y < Count - 1; y++)
 					_array[y] = _array[y + 1];
 			}
 			_position -= toRemove;