Coverity Check: codegenerators: Fixing unchecked dynamic_casts

This fixes Coverity check CIDs: 71404, 71405, 71409, 71415, 71430,
71432, 71434, 71435, 71438, 71439, 71446, 71453, 71456, 71457,
71458, 71460

Coverity reported lots of errors (> 50) of the same type:

T *var = dynamic_cast<T>(a);
foo(var);

var was never checked against NULL.

CCBUG:340646
REVIEW:124658