Give readability names up on a copy

The names that make a primitive value readable were written into the
ArgumentNames array the call carries, so the step that gives them up again
found them still there: for any call that already carried names of its
own, turning them off was a no-op, and the ladder went on to cast instead.

Assisted-by: Claude:claude-opus-5[1m]:Claude Code

ICSharpCode.Decompiler/CSharp/CallBuilder.cs

@@ -77,10 +77,11 @@ namespace ICSharpCode.Decompiler.CSharp
 						&& !ParameterNames.Any(string.IsNullOrEmpty))
 				{
 					Debug.Assert(skipCount == 0);
-					if (argumentNames == null)
+					// On a copy: giving these names up again must leave the ones that order the
-					{
+					// arguments untouched.
-						argumentNames = new string[Arguments.Length];
+					argumentNames = argumentNames == null
-					}
+						? new string[Arguments.Length]
+						: (string[])argumentNames.Clone();
 
 					for (int i = 0; i < Arguments.Length; i++)
 					{