Fix #868: incorrect inlining of readonly fields.

ICSharpCode.Decompiler.Tests/TestCases/Correctness/ValueTypeCall.cs

@@ -81,6 +81,9 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Correctness
 			MutValueType v = MutableField;
 			v.Increment();
 			Console.WriteLine("Final value in MutableField: " + MutableField.val);
+			// Read-only field copies cannot be inlined for static methods:
+			MutValueType localCopy = ReadonlyField;
+			RefParameter(ref localCopy);
 		}
 		
 		static void Box()

ICSharpCode.Decompiler/IL/Transforms/ILInlining.cs

@@ -209,7 +209,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 						// allow inlining field access only if it's a readonly field
 						IField f = (((LdObj)inlinedExpression).Target as IInstructionWithFieldOperand)?.Field;
 						if (f != null && f.IsReadOnly)
-							return true;
+							break;
 						return f != null && f.IsReadOnly;
 					case OpCode.Call:
 						var m = ((CallInstruction)inlinedExpression).Method;