Clock: Fix bugs when resuming the clock.

Clock: Fix bugs when resuming the clock.

Adam Elliot writes:

>  Automatically resuming the clock after an Emacs restart
>  fails under the following cases:
>
>  1. If org-log-states-order-reversed set to t (default), and
>     a state change line precedes the clock line to resume.
>     Error message is "Cannot restart clock because task does
>     not contain unfinished clock".
>
[...]
>  2. If org-log-states-order-reversed set to nil.  Error
>     message is the same.  Reason: point is placed *after*
>     last clock line and so fails looking-at test.
>

This commit fixes the problem, in a slightly different way
than Adam proposed.  Instead of trying to fix the old way to
find the position of the clock, we now simple search the
entry if there is an unfinished clock and go there.  Since
new clocks are added before older ones, this should be a
safe bet.