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

src/lib/eo/Eo.h

@@ -1231,6 +1231,7 @@ typedef struct _Efl_Object_Call_Cache
 // hits.
 #define EFL_FUNC_COMMON_OP_END(Obj, Name, DefRet) \
 __##Name##_op_create: \
+   if (EINA_UNLIKELY(___cache.op != EFL_NOOP)) memset(&___cache, 0, sizeof(___cache)); \
    ___cache.op = _efl_object_op_api_id_get(EFL_FUNC_COMMON_OP_FUNC(Name), Obj, #Name, __FILE__, __LINE__); \
    if (___cache.op == EFL_NOOP) return DefRet; \
    ___cache.generation = _efl_object_init_generation; \

src/lib/eo/eo.c

@@ -498,6 +498,7 @@ ok_klass_back:
                        call->func = func->func;
                        if (is_obj)
                          call->data = (char *)obj + cache->off[i].off;
+                       if (EINA_UNLIKELY(!call->func)) goto err_cache_op;
                        return EINA_TRUE;
                     }
                }