[bugpoint] ReduceCrashingFunctions::TestFuncs - fix dereference of null point...

[bugpoint] ReduceCrashingFunctions::TestFuncs - fix dereference of null point static analyzer warning

Alias.getAliaseeObject() shouldn't be null, do use dyn_cast instead of dyn_cast_or_null

Also, remove redundant `else if (!F)` test - that is always true at the point in the if-else chain