Bug fix: NullPointerException for input files without seed mechanisms
Bug fix: NullPointerException for input files without seed mechanisms

This commit fixes the NPE that GRM found.  The problem was that MRH assumed
there would always be a seedMechanism instance, and therefore always a
reactionSet() to extract and send to the ODESolver and CHEMKIN classes.

Thanks Greg for finding this.

KEHANG/RMG-Java,ReactionMechanismGenerator/RMG-Java,enochd/RMG-Java,KEHANG/RMG-Java,KEHANG/RMG-Java,enochd/RMG-Java,rwest/RMG-Java,connie/RMG-Java,ReactionMechanismGenerator/RMG-Java,nyee/RMG-Java,connie/RMG-Java,enochd/RMG-Java,connie/RMG-Java,keceli/RMG-Java,connie/RMG-Java,jwallen/RMG-Java,rwest/RMG-Java,rwest/RMG-Java,nyee/RMG-Java,KEHANG/RMG-Java,rwest/RMG-Java,keceli/RMG-Java,enochd/RMG-Java,jwallen/RMG-Java,keceli/RMG-Java,faribas/RMG-Java,enochd/RMG-Java,KEHANG/RMG-Java,jwallen/RMG-Java,jwallen/RMG-Java,rwest/RMG-Java,faribas/RMG-Java,KEHANG/RMG-Java,nyee/RMG-Java,nyee/RMG-Java,faribas/RMG-Java,jwallen/RMG-Java,ReactionMechanismGenerator/RMG-Java,enochd/RMG-Java,faribas/RMG-Java,keceli/RMG-Java,ReactionMechanismGenerator/RMG-Java,jwallen/RMG-Java,ReactionMechanismGenerator/RMG-Java,connie/RMG-Java,keceli/RMG-Java,nyee/RMG-Java,nyee/RMG-Java,keceli/RMG-Java