Fix #3367: Add extra validation to TransformDecimalCtorToConstant to prevent crashes with obfuscated assemblies.

Author: siegfriedpammer

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

@@ -260,6 +260,15 @@ public byte Issue2166b(int x)
 			return (byte)(x & 0x10);
 		}
 
+		public decimal Issue3367()
+		{
+#if CS70
+			return new decimal(0, 0, 0, isNegative: false, 29);
+#else
+			return new decimal(0, 0, 0, false, 29);
+#endif
+		}
+
 		private void ExpectUInt64(ulong _)
 		{
 

ICSharpCode.Decompiler/IL/Transforms/EarlyExpressionTransforms.cs

@@ -213,7 +213,7 @@ bool TransformDecimalCtorToConstant(NewObj inst, out LdcDecimal result)
 				int lo, mid, hi, isNegative, scale;
 				if (args[0].MatchLdcI4(out lo) && args[1].MatchLdcI4(out mid) &&
 					args[2].MatchLdcI4(out hi) && args[3].MatchLdcI4(out isNegative) &&
-					args[4].MatchLdcI4(out scale))
+					args[4].MatchLdcI4(out scale) && scale <= 28)
 				{
 					result = new LdcDecimal(new decimal(lo, mid, hi, isNegative != 0, (byte)scale));
 					return true;