Fix stack corruption in TryEmitExportParameterArgument

LoadArgument + LoadConstantI4(0) were emitted unconditionally before the
switch statement. When exportKind is Unspecified (the default for
parameters without [ExportParameter] attributes), the method returned
false without consuming those two stack values, corrupting the IL
evaluation stack.

Move the LoadArgument + LoadConstantI4(0) into each case block so they
are only emitted when the method will also emit the consuming Call.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: simonrozsival

src/Microsoft.Android.Sdk.TrimmableTypeMap/Generator/ExportMethodDispatchEmitter.cs

@@ -284,20 +284,25 @@ void ThrowIfUnsupportedManagedType (string managedTypeName)
 
 	bool TryEmitExportParameterArgument (InstructionEncoder encoder, ExportParameterKindInfo exportKind, int argumentIndex)
 	{
-		encoder.LoadArgument (argumentIndex);
-		encoder.LoadConstantI4 (0);
-
 		switch (exportKind) {
 			case ExportParameterKindInfo.InputStream:
+				encoder.LoadArgument (argumentIndex);
+				encoder.LoadConstantI4 (0);
 				encoder.Call (_context.InputStreamInvokerFromJniHandleRef);
 				return true;
 			case ExportParameterKindInfo.OutputStream:
+				encoder.LoadArgument (argumentIndex);
+				encoder.LoadConstantI4 (0);
 				encoder.Call (_context.OutputStreamInvokerFromJniHandleRef);
 				return true;
 			case ExportParameterKindInfo.XmlPullParser:
+				encoder.LoadArgument (argumentIndex);
+				encoder.LoadConstantI4 (0);
 				encoder.Call (_context.XmlPullParserReaderFromJniHandleRef);
 				return true;
 			case ExportParameterKindInfo.XmlResourceParser:
+				encoder.LoadArgument (argumentIndex);
+				encoder.LoadConstantI4 (0);
 				encoder.Call (_context.XmlResourceParserReaderFromJniHandleRef);
 				return true;
 			default: