AIX image buffer allocation failure

On an AIX 4.3 system the command "image create
photo" fails in file tkImgPhoto.c, function,
ImgPhotoSetSize, line 2656, when attemptckalloc() is
called. AIX and some other systems (Tru64) return
NULL from an alloc call for 0 size. This problem affects
only Tk 8.4. The fix that I have successfully tested is

if ((width != masterPtr->width) || (height != masterPtr-
>height) || (masterPtr->pix24 == NULL) {
unsigned size;
size = height * pitch;
if (size > 0) {
newPix24 = (unsigned char *) attemptckalloc(size);
if (newPix24 == NULL) { return TCL_ERROR; }
}
else { newPix24 = NULL; }
}