Silence Coverity error 1298872
Silence Coverity error 1298872

Coverity complains that in parallel.cpp's makeHeapAllocations(), a SymExpr whose
fields we access could be NULL.  I think this is very unlikely, but we should
catch it if it does happen, so I'm adding an assertion.

chizarlicious/chapel,CoryMcCartan/chapel,chizarlicious/chapel,CoryMcCartan/chapel,CoryMcCartan/chapel,CoryMcCartan/chapel,chizarlicious/chapel,chizarlicious/chapel,hildeth/chapel,chizarlicious/chapel,CoryMcCartan/chapel,chizarlicious/chapel,hildeth/chapel,CoryMcCartan/chapel,hildeth/chapel,hildeth/chapel,CoryMcCartan/chapel,hildeth/chapel,hildeth/chapel,hildeth/chapel,chizarlicious/chapel