Simplify the cursor-invalid code.  This shouldn't be a functionality
change, but it consolidates the tests for a "valid" page slot.  I
can't figure out why the tests were split into two parts (one set
done search didn't return an insert object , and the other done if
search returned an insert object but didn't find a visible update,
or search didn't return an insert object.  The test combination may
not be necessary, but it's not going to cost anything and should be
more resiliant to changes in the search routines.   Reference #1062.