Remove unexplained segfault for pow(x,a) with a < 0.
Remove unexplained segfault for pow(x,a) with a < 0.

robertodr/xcfun,robertodr/xcfun,bast/xcfun,dftlibs/xcfun,robertodr/xcfun,dftlibs/xcfun,robertodr/xcfun,bast/xcfun,dftlibs/xcfun,bast/xcfun,dftlibs/xcfun,bast/xcfun