procedure SaveToStreamAll(Stream: TStream; imageCompression: TIOFileType);
Saves all layers and vectorial objects in one single stream block. This is like consecutive calls to LayersSaveToXXX and SaveToFileIEV.
ImageCompression specifies how compress the background image and the layers (cannot be ioTIFF). If ImageCompression is -1, the image is saved using an internal format which preserves pixel format and alphachannel.
Result will be false if an unexpected error was encountered while saving (Aborting
will be true).