punch-alternating: prevent punching all extents

punch-alternating: prevent punching all extents

If by any chance the punch size is >= the interval, we end up punching
everything, zeroing out the file.

As this is not a tool to dealloc the whole file, so force the user to
pass a configuration that won't cause it to happen.

Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>