libtiff: Fix unsigned vs signed comparison warning.

third_party/libtiff/tif_pixarlog.c

Index: third_party/libtiff/tif_pixarlog.c
diff --git a/third_party/libtiff/tif_pixarlog.c b/third_party/libtiff/tif_pixarlog.c
index 0674fa48d667a89b7687d3edd9addb77cc7cb184..29535d31ee1d8fb7dc6bf91086a84299148e912e 100644
--- a/third_party/libtiff/tif_pixarlog.c
+++ b/third_party/libtiff/tif_pixarlog.c
@@ -784,7 +784,7 @@ PixarLogDecode(TIFF* tif, uint8* op, tmsize_t occ, uint16 s)
 		return (0);
 	}
 	/* Check that we will not fill more than what was allocated */
-	if (sp->stream.avail_out > sp->tbuf_size)
+	if ((tmsize_t)sp->stream.avail_out > sp->tbuf_size)
 	{
 		TIFFErrorExt(tif->tif_clientdata, module, "sp->stream.avail_out > sp->tbuf_size");
 		return (0);