eo: Fix crashes with call cache after init cycle

eo: Fix crashes with call cache after init cycle

It's not enough to check the init generation count, if the cache data is
not reset properly.

This patch adds safety in two ways:
 1. Actually reset the op call cache when we detect a new generation
 2. Verify that we don't return NULL function pointer

The 1st point is absolutely necessary, 2nd is optional (extra cost of
one if()).

@fix