Fix #1563: `Unexpected return in MoveNext()` when mixed `using` and more than one `yield break`

Roslyn re-uses the same "this.Finally(); return v;" block for both "yield break;" instructions, so the yield break pattern needs to support multiple stores to the helper variable.

ICSharpCode.Decompiler.Tests/TestCases/Pretty/YieldReturn.cs

@@ -335,5 +335,26 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 				yield return val;
 			}
 		}
+
+		public static IEnumerable<int> MultipleYieldBreakInTryFinally(int i)
+		{
+			try {
+				if (i == 2) {
+					yield break;
+				}
+
+				while (i < 40) {
+					if (i % 2 == 0) {
+						yield break;
+					}
+					i++;
+
+					yield return i;
+				}
+			} finally {
+				Console.WriteLine("finally");
+			}
+			Console.WriteLine("normal exit");
+		}
 	}
 }

ICSharpCode.Decompiler/IL/ControlFlow/YieldReturnDecompiler.cs

@@ -810,14 +810,15 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 						break;
 					case Leave leave:
 						if (leave.MatchReturn(out var value)) {
+							bool validYieldBreak = value.MatchLdcI4(0);
 							if (value.MatchLdLoc(out var v)
 								&& (v.Kind == VariableKind.Local || v.Kind == VariableKind.StackSlot)
-								&& v.StoreInstructions.Count == 1
-								&& v.StoreInstructions[0] is StLoc stloc) {
-								returnStores.Add(stloc);
-								value = stloc.Value;
+								&& v.StoreInstructions.All(store => store is StLoc stloc && stloc.Value.MatchLdcI4(0)))
+							{
+								validYieldBreak = true;
+								returnStores.AddRange(v.StoreInstructions.Cast<StLoc>());
 							}
-							if (value.MatchLdcI4(0)) {
+							if (validYieldBreak) {
 								// yield break
 								leave.ReplaceWith(new Leave(newBody).WithILRange(leave));
 							} else {