verify client in download handler

[Hitenjain14]

Changes

Fixes

Tests

Tasks to complete before merging PR:

• [ ] Ensure system tests are passing. If not Run them manually to check for any regressions :clipboard:
• [ ] Do any new system tests need added to test this change? do any existing system tests need updated? If so create a PR at 0chain/system_test
• [ ] Merge your system tests PR to master AFTER merging this PR

Associated PRs (Link as appropriate):

• 0chain:
• gosdk: https://github.com/0chain/gosdk/pull/1378
• system_test: https://github.com/0chain/system_test/pull/995
• zboxcli:
• zwalletcli:
• Other: ...

[codecov-commenter]

Codecov Report

Attention: 28 lines in your changes are missing coverage. Please review.

Comparison is base (cce361c) 14.40% compared to head (9f54632) 14.46%.

Files	Patch %	Lines
...et/blobbercore/handler/object_operation_handler.go	44.00%	11 Missing and 3 partials :warning:
.../0chain.net/blobbercore/handler/storage_handler.go	55.17%	11 Missing and 2 partials :warning:
code/go/0chain.net/blobbercore/handler/context.go	50.00%	1 Missing :warning:

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## staging #1378 +/- ## =========================================== + Coverage 14.40% 14.46% +0.06% =========================================== Files 177 177 Lines 19859 19891 +32 =========================================== + Hits 2861 2878 +17 - Misses 16642 16653 +11 - Partials 356 360 +4 ``` | [Flag](https://app.codecov.io/gh/0chain/blobber/pull/1378/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=0chain) | Coverage Δ | | |---|---|---| | [Unit-Tests](https://app.codecov.io/gh/0chain/blobber/pull/1378/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=0chain) | `14.46% <56.92%> (+0.06%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=0chain#carryforward-flags-in-the-pull-request-comment) to find out more.

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