avoid extra tile info write in TIFFWriteDirectory()

ChangeLog

@@ -1,5 +1,12 @@
 2007-11-02  Frank Warmerdam  <warmerdam@pobox.com>
 
+	* tif_dirwrite.c: Try to avoid writing out a full readbuffer of tile
+	data when writing the directory just because we have BEENWRITING at
+	some point in the past.  This was causing odd junk to be written out
+	in a tile of data when a single tile had an interleaving of reading 
+	and writing with reading last.  (highlighted by gdal 
+	autotest/gcore/tif_write.py test 7. 
+
 	* tif_predict.c: use working buffer in PredictorEncodeTile to avoid
 	modifying callers buffer. 
 	http://trac.osgeo.org/gdal/ticket/1965

libtiff/tif_dirwrite.c

@@ -323,6 +323,8 @@ TIFFWriteDirectorySec(TIFF* tif, int isimage, int imagedone, uint64* pdiroff)
 	 */
 	if (imagedone)
 	{
+                tmsize_t orig_rawcc = tif->tif_rawcc;
+
 		if (tif->tif_flags & TIFF_POSTENCODE)
 		{
 			tif->tif_flags &= ~TIFF_POSTENCODE;
@@ -336,9 +338,12 @@ TIFFWriteDirectorySec(TIFF* tif, int isimage, int imagedone, uint64* pdiroff)
 		(*tif->tif_close)(tif);       /* shutdown encoder */
 		/*
 		 * Flush any data that might have been written
-		 * by the compression close+cleanup routines.
+		 * by the compression close+cleanup routines.  But
+                 * be careful not to write stuff if we didn't add data
+                 * in the previous steps as the "rawcc" data may well be
+                 * a previously read tile/strip in mixed read/write mode.
 		 */
-		if (tif->tif_rawcc > 0
+		if (tif->tif_rawcc > 0 && tif->tif_rawcc != orig_rawcc
 		    && (tif->tif_flags & TIFF_BEENWRITING) != 0
 		    && !TIFFFlushData1(tif))
 		{