Fix a conditional check. (size - tc->size > 0) is always true if size and tc->size...

Fix a conditional check. (size - tc->size > 0) is always true if size and tc->size are unsigned.

Replace with (size > tc->size).

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Simo Sorce <idra@samba.org>