Fix error with elasticsearch(sniff_on_start=True)

[basepi]

What does this pull request do?

Checks if the span object is non-None before trying to access its context.

No test attached. I've been unable to get one to fail even without the fix....it may be that we're missing something in the user's edge case. In any case, I think this is a change that should fix the user's issue, and is extremely low-risk. So I think we can forgo the test.

Related issues

Closes #1615

[ghost]

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• Start Time: 2022-08-22T18:07:21.003+0000

• Duration: 31 min 16 sec

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Test	Results
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Skipped	3420
Total	8394

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[ghost]

🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	100.0% (68/68)	💚
Files	100.0% (227/227)	💚
Classes	100.0% (227/227)	💚
Lines	89.755% (17452/19444)	👎 -0.163
Conditionals	77.18% (3186/4128)	👎 -0.101

[basepi]

/test full

[trentm]

Seems reasonable (not knowing the agent internals at all well :). It looks like redis.py and aioredis.py have a similar guard.

There is a call to execution_context.get_span() in "asyncio/elasticsearch.py" as well that doesn't have a guard. Perhaps that should eventually get it as well.