Fix NullReferenceException in type analysis.

Closes #393, #386, #403.

ICSharpCode.Decompiler/ILAst/TypeAnalysis.cs

@@ -539,6 +539,8 @@ namespace ICSharpCode.Decompiler.ILAst
 						if (forceInferChildren)
 							InferTypeForExpression(expr.Arguments[1], typeSystem.Int32);
 						TypeReference type = NumericPromotion(InferTypeForExpression(expr.Arguments[0], null));
+						if (type == null)
+							return null;
 						TypeReference expectedInputType = null;
 						switch (type.MetadataType) {
 							case MetadataType.Int32:

ICSharpCode.Decompiler/Tests/TypeAnalysisTests.cs

@@ -150,4 +150,10 @@ public class TypeAnalysisTests
 	{
 		return Math.Abs(a - b);
 	}
+	
+	public void Bug393(int valuePos)
+	{
+		if ((0x2A >> (valuePos++)) == 0)
+			return;
+	}
 }