Patch for bug #603081: failure to guard against bogus SamplesPerPixel

when converting a YCbCr image to RGB.

This patch duplicates into PickContigCase() a safety check that already

existed in PickSeparateCase().

Filed upstream at http://bugzilla.maptools.org/show_bug.cgi?id=2216

diff -Naur tiff-3.9.2.orig/libtiff/tif_getimage.c tiff-3.9.2/libtiff/tif_getimage.c

--- tiff-3.9.2.orig/libtiff/tif_getimage.c	2009-08-30 12:21:46.000000000 -0400

+++ tiff-3.9.2/libtiff/tif_getimage.c	2010-06-11 12:06:47.000000000 -0400

@@ -2397,7 +2397,7 @@

 			}

 			break;

 		case PHOTOMETRIC_YCBCR:

-			if (img->bitspersample == 8)

+			if ((img->bitspersample==8) && (img->samplesperpixel==3))

 			{

 				if (initYCbCrConversion(img)!=0)

 				{