http2: protects client against stream not found

[birenroy]

There are similar checks already on the server side:

envoy/source/common/http/http2/codec_impl.cc

Line 2294 in 34838db

if (stream_ptr != nullptr) {

Commit Message: http2: protects client against stream not found
Additional Description:
Risk Level: low
Testing: ran unit and integration tests locally
Docs Changes:
Release Notes:
Platform Specific Features:

[repokitteh-read-only]

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🐱

Caused by: #36573 was opened by birenroy.

see: more, trace.

[birenroy]

/assign @alyssawilk
/assign @RyanTheOptimist

[alyssawilk]

I think you had trouble e2e testing but I suspect you could unit test this
/wait-any

[RyanTheOptimist]

Can we get a unit test for this