fix: allow pools to not be defined without raising exceptions

[StephenHulme]

Allow pools to not be defined without breaking all javascript in the page: user errors should not cause syntax errors.

Changes proposed in this pull request

• stop processing JS if pool is undefined or empty-string

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[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.

Project coverage is 77.95%. Comparing base (40ef006) to head (60b4bba). Report is 3 commits behind head on develop.

Files with missing lines	Patch %	Lines
app/frontend/javascript/legacy_scripts_a.js	0.00%	4 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #2005 +/- ## =========================================== - Coverage 77.97% 77.95% -0.02% =========================================== Files 463 463 Lines 17708 17711 +3 Branches 225 225 =========================================== Hits 13807 13807 - Misses 3899 3902 +3 Partials 2 2 ``` | [Flag](https://app.codecov.io/gh/sanger/limber/pull/2005/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=sanger) | Coverage Δ | | |---|---|---| | [javascript](https://app.codecov.io/gh/sanger/limber/pull/2005/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=sanger) | `69.66% <0.00%> (-0.02%)` | :arrow_down: | | [pull_request](https://app.codecov.io/gh/sanger/limber/pull/2005/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=sanger) | `77.95% <0.00%> (-0.02%)` | :arrow_down: | | [push](https://app.codecov.io/gh/sanger/limber/pull/2005/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=sanger) | `77.95% <0.00%> (-0.02%)` | :arrow_down: | | [ruby](https://app.codecov.io/gh/sanger/limber/pull/2005/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=sanger) | `91.16% <ø> (ø)` | | 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=sanger#carryforward-flags-in-the-pull-request-comment) to find out more.

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[StephenHulme]

Stalled as this should ideally be tested against the real-life scenario before merging in - maybe it can be deployed to training?

[codeclimate[bot]]

Code Climate has analyzed commit 60b4bba2 and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 100.0% (50% is the threshold).

This pull request will bring the total coverage in the repository to 91.1% (0.0% change).

View more on Code Climate.

[StephenHulme]

Tested successfully in training comparing against uat.