Merge "adb: defuse CHECK on IOVector::append of an empty block."

    // Add a nonempty block to the chain.

    // The end of the chain must be a complete block (i.e. end_offset_ == 0).

    void append(std::unique_ptr<const block_type> block) {

        CHECK_NE(0ULL, block->size());

        if (block->size() == 0) {

            return;

        }

        CHECK_EQ(0ULL, end_offset_);

        chain_length_ += block->size();

        chain_.emplace_back(std::move(block));