mapped_io: fix mapped_eof on windows

The mmaped IO implementation on windows does not always increment `pos`
on each `getByte`. It relies on an incrementing pointer `iter`, and
update `pos` only when a new chunk gets maped.

However, mmaped_eof was only considering `pos` and not `iter`, and
therefore was sometimes incorrectly returning false until a later call
to `getByte` would update `pos`.

Author: alpire

src/mappedio.c

@@ -156,7 +156,7 @@ static int TIDY_CALL mapped_getByte( void *sourceData )
 static Bool TIDY_CALL mapped_eof( void *sourceData )
 {
     MappedFileSource *data = sourceData;
-    return ( data->pos >= data->size );
+    return ( data->pos + (data->iter - data->view) >= data->size );
 }
 
 static void TIDY_CALL mapped_ungetByte( void *sourceData, byte ARG_UNUSED(bt) )