[FIX] models: avoid recursive `recompute()` in method `unlink()`

This fixes an issue when a one2many computed field is recomputed: all computed
lines are created twice.

Consider a simple case, where the value of the field is a single line.  The
execution goes as follows:

 * invoke `recompute()`
    * write value `[(5,), (0, 0, vals)]` to the field
       * command `(5,)`: invoke `unlink()`
          * delete existing lines
          * invoke `recompute()`
             * write value `[(5,), (0, 0, vals)]` to the field
                * command `(5,)`: invoke `unlink()`
                   * no more existing lines, return
                * command `(0, 0, vals)`: invoke `create()`
                   * create a new line
             * mark the field as recomputed
       * command `(0, 0, vals)`: invoke `create()`
          * create a new line
    * mark the field as recomputed

There is a recursive call to `recompute()` inside `unlink()` that recomputes
the field while it is being written.  The fix simply prevents the recursive
call to `recompute()`, just like in methods `create()` and `write()`.

0 files changed, 0 insertions, 0 deletions