Fix failure for OPTIMIZED parallel evaluation.

When parallel calculation is done multiple times with the same
calculator object the second and subsequent results are zero
because of OPTIMIZED evaluation.

Solution: Always use a copy of calculator object for partial job.

Author: pavoljuhas

diffpy/srreal/parallel.py

@@ -167,6 +167,8 @@ def _parallelData(kwd):
     '''Helper for calculating and fetching raw results from a worker node.
     '''
     pqobj = kwd['pqobj']
+    if pqobj.evaluatortype == 'OPTIMIZED':
+        pqobj = copy.copy(pqobj)
     pqobj._setupParallelRun(kwd['cpuindex'], kwd['ncpu'])
     pqobj.eval()
     return pqobj._getParallelData()