prune failed after reset

[toomish]

After reset call prune failed when tries to delete many items at once.

cm <- cachem::cache_mem(max_size = object.size(1:100))

for (key in c("a", "b"))
        cm$set(key, TRUE)

cm$reset()
cm$set("c", 1:100)

Results:

Error in vapply(keys, remove_one_, TRUE) : values must be length 1,
 but FUN(X[[1]]) result is length 0
Calls: <Anonymous> -> prune -> remove_ -> vapply