Fix #1338: KeyNotFoundException in SwitchDetection.AnalyzeControlFlow()

ICSharpCode.Decompiler/IL/ControlFlow/SwitchDetection.cs

@@ -350,10 +350,12 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 				if (!s.Value.MatchBranch(out var block)) 
 					continue;
 
+				if (block.Parent == currentContainer) {
 					var node = controlFlowGraph.GetNode(block);
 					if (!loopContext.MatchContinue(node))
 						caseNodes.Add(node);
 				}
+			}
 
 			AddNullCase(flowNodes, caseNodes);