Fixed dmdfe generated class invariant calls. Also insert proper "this !is null" check before it. Fixed invariant* dstress regressions and generally seems like a good idea. Hope I didn't break anything.. minitests run fine!

module typeinfos2;

import
typeinfo2.ti_AC,
typeinfo2.ti_Adouble,
typeinfo2.ti_Afloat,
typeinfo2.ti_Ag,
typeinfo2.ti_Aint,
typeinfo2.ti_Along,
typeinfo2.ti_Areal,
typeinfo2.ti_Ashort,
typeinfo2.ti_C;