Fix failure to use clamp_row_est() for parallel joins.
Commit
0c2070cefa0e5d097b715c9a3b9b5499470019aa neglected to use
clamp_row_est() where it should have done so.
Patch by me. Report by Amit Kapila.
Discussion: http://postgr.es/m/CAA4eK1KPm8RYa1Kun3ZmQj9pb723b-EFN70j47Pid1vn3ByquA@mail.gmail.com