AFTER two years of heartache, Melrose Place stars Josie Bissett and her hubby Rob Estes are celebrating the joyous birth of a baby boy.
     Their first child, Mason Tru, came into the world July 21 in L.A. "Rob and Josie are on cloud nine," says a close pal. "They're already talking about having another!"
     As GLOBE reported in July 1997, Josie, 28, and 36-year-old Rob were devastated by a tragic miscarriage. For the last two years, they've struggled to conceive, finally consulting a fertility expert.
     "Tests showed Josie lacked an antibody that protects a fetus from rejection," says a source. "Once the problem was detected, it only took one procedure to ensure her next pregnancy's success."