Fix for unintentional removal of some leave instructions (#96)

This will keep 2 leave instructions, but it's jump anyway, no harm done. Upstream harmony makes it this way.
These instructions are added after all transpilers have already been applied, and repatching takes original instructions anyway.
And, if someone wants to, they can find a way to remove these duplicates without offset shifting later on.

Fixes #65 and Closes #77

Harmony/Internal/Patching/ILManipulator.cs

@@ -340,17 +340,13 @@ public void WriteTo(MethodBody body, MethodBase original = null)
 		var newInstructions = ApplyTranspilers(cil, original, vDef => il.GetLocal(vDef), il.DefineLabel);
 
 		// Step 2: Emit code
-		foreach (var (cur, next) in newInstructions.Pairwise())
+		foreach (var cur in newInstructions)
 		{
 			cur.labels.ForEach(l => il.MarkLabel(l));
 			cur.blocks.ForEach(b => il.MarkBlockBefore(b));
 
 			// We need to handle exception handler opcodes specially because ILProcessor emits them automatically
-			// Case 1: leave + start or end of exception block => ILProcessor generates leave automatically
-			if ((cur.opcode == SRE.OpCodes.Leave || cur.opcode == SRE.OpCodes.Leave_S) &&
-			    (cur.blocks.Count > 0 || next?.blocks.Count > 0))
-				goto mark_block;
-			// Case 2: endfilter/endfinally and end of exception marker => ILProcessor will generate the correct end
+			// Case: endfilter/endfinally and end of exception marker => ILProcessor will generate the correct end
 			if ((cur.opcode == SRE.OpCodes.Endfilter || cur.opcode == SRE.OpCodes.Endfinally) && cur.blocks.Count > 0)
 				goto mark_block;
 			// Other cases are either intentional leave or invalid IL => let them be processed and let JIT generate correct exception

Harmony/Tools/Extensions.cs

@@ -595,30 +595,6 @@ internal static Dictionary<K, V> TransformKeys<K, V>(this Dictionary<K, V> origD
 				dict.Add(transform(pair.Key), pair.Value);
 			return dict;
 		}
-
-		// Iterates the enumerable pairwise, i.e. by returning tuple (current, next)
-		internal static IEnumerable<(T, T)> Pairwise<T>(this IEnumerable<T> self)
-		{
-			var isFirst = true;
-			T prev = default;
-
-			foreach (var e in self)
-				if (isFirst)
-				{
-					prev = e;
-					isFirst = false;
-				}
-				else
-				{
-					yield return (prev, e);
-					prev = e;
-				}
-
-			if (isFirst)
-				yield break;
-
-			yield return (prev, default);
-		}
 	}
 
 	/// <summary>General extensions for collections</summary>