[fix] [exporterhelper] Fix nil ptr dereference on storage stop

[fredthomsen]

When persistent queue fails to start, for example due to bad permissions, then persistent storage does not get allocated. Thus, ensure stop storage method is only called if actually initialized.

Description:
Fixing a bug that resulted in panic when de-referencing nil pointer. The issue is that in the persistent queue fail to start due to say bad folder permissions, then the Start method does not actually set the associated persistent storage, and thus when shutting down it tries to stop the storage and panics.

The traceback appeared as follows:

otc-otc-1  | 2023-10-21T05:10:03.187Z   info    extensions/extensions.go:33     Starting extensions...
otc-otc-1  | 2023-10-21T05:10:03.187Z   info    extensions/extensions.go:36     Extension is starting...        {"kind": "extension", "name": "file_storage/sl1receiver"}
otc-otc-1  | 2023-10-21T05:10:03.187Z   info    extensions/extensions.go:43     Extension started.      {"kind": "extension", "name": "file_storage/sl1receiver"}
otc-otc-1  | 2023-10-21T05:10:03.187Z   info    extensions/extensions.go:36     Extension is starting...        {"kind": "extension", "name": "file_storage/exporter_queue"}
otc-otc-1  | 2023-10-21T05:10:03.187Z   info    extensions/extensions.go:43     Extension started.      {"kind": "extension", "name": "file_storage/exporter_queue"}
otc-otc-1  | 2023-10-21T05:10:03.187Z   info    extensions/extensions.go:36     Extension is starting...        {"kind": "extension", "name": "memory_ballast"}
otc-otc-1  | 2023-10-21T05:10:03.388Z   info    ballastextension@v0.87.0/memory_ballast.go:41   Setting memory ballast  {"kind": "extension", "name": "memory_ballast", "MiBs": 6419}
otc-otc-1  | 2023-10-21T05:10:03.389Z   info    extensions/extensions.go:43     Extension started.      {"kind": "extension", "name": "memory_ballast"}
otc-otc-1  | 2023-10-21T05:10:03.390Z   info    service@v0.87.0/service.go:178  Starting shutdown...
otc-otc-1  | panic: runtime error: invalid memory address or nil pointer dereference
otc-otc-1  | [signal SIGSEGV: segmentation violation code=0x1 addr=0x10 pc=0xeb5782]
otc-otc-1  |
otc-otc-1  | goroutine 1 [running]:
otc-otc-1  | go.opentelemetry.io/collector/exporter/exporterhelper/internal.(*persistentContiguousStorage).stop(0x0)
otc-otc-1  |    go.opentelemetry.io/collector/exporter@v0.87.0/exporterhelper/internal/persistent_storage.go:196 +0x22
otc-otc-1  | go.opentelemetry.io/collector/exporter/exporterhelper/internal.glob..func1(0xc000a90540?)
otc-otc-1  |    go.opentelemetry.io/collector/exporter@v0.87.0/exporterhelper/internal/persistent_queue.go:19 +0x17
otc-otc-1  | go.opentelemetry.io/collector/exporter/exporterhelper/internal.(*persistentQueue).Stop.func1()
otc-otc-1  |    go.opentelemetry.io/collector/exporter@v0.87.0/exporterhelper/internal/persistent_queue.go:94 +0x42
otc-otc-1  | sync.(*Once).doSlow(0xc000b5b128?, 0xc000b5b0e0?)
otc-otc-1  |    sync/once.go:74 +0xbf
otc-otc-1  | sync.(*Once).Do(...)
otc-otc-1  |    sync/once.go:65
otc-otc-1  | go.opentelemetry.io/collector/exporter/exporterhelper/internal.(*persistentQueue).Stop(0x38dd560?)
otc-otc-1  |    go.opentelemetry.io/collector/exporter@v0.87.0/exporterhelper/internal/persistent_queue.go:90 +0x3c
otc-otc-1  | go.opentelemetry.io/collector/exporter/exporterhelper.(*queueSender).shutdown(0xc00092a3f0)
otc-otc-1  |    go.opentelemetry.io/collector/exporter@v0.87.0/exporterhelper/queue_sender.go:161 +0x78
otc-otc-1  | go.opentelemetry.io/collector/exporter/exporterhelper.(*baseExporter).Shutdown(0xc00052e000, {0x4c563b0, 0x72ffec0})
otc-otc-1  |    go.opentelemetry.io/collector/exporter@v0.87.0/exporterhelper/common.go:221 +0x4d
otc-otc-1  | go.opentelemetry.io/collector/service/internal/graph.(*Graph).ShutdownAll(0xc000c547e0, {0x4c563b0, 0x72ffec0})
otc-otc-1  |    go.opentelemetry.io/collector/service@v0.87.0/internal/graph/graph.go:422 +0x1c3
otc-otc-1  | go.opentelemetry.io/collector/service.(*Service).Shutdown(0xc000a3dc20, {0x4c563b0, 0x72ffec0})
otc-otc-1  |    go.opentelemetry.io/collector/service@v0.87.0/service.go:184 +0xd7
otc-otc-1  | go.opentelemetry.io/collector/otelcol.(*Collector).setupConfigurationComponents(0xc000b3a000, {0x4c563b0, 0x72ffec0})
otc-otc-1  |    go.opentelemetry.io/collector/otelcol@v0.87.0/collector.go:187 +0x6ca
otc-otc-1  | go.opentelemetry.io/collector/otelcol.(*Collector).Run(0xc000b3a000, {0x4c563b0, 0x72ffec0})
otc-otc-1  |    go.opentelemetry.io/collector/otelcol@v0.87.0/collector.go:221 +0x52
otc-otc-1  | go.opentelemetry.io/collector/otelcol.NewCommand.func1(0xc000b24000, {0x436812e?, 0x7?, 0x436307f?})
otc-otc-1  |    go.opentelemetry.io/collector/otelcol@v0.87.0/command.go:27 +0x74
otc-otc-1  | github.com/spf13/cobra.(*Command).execute(0xc000b24000, {0xc000072050, 0x1, 0x1})
otc-otc-1  |    github.com/spf13/cobra@v1.7.0/command.go:940 +0x87c
otc-otc-1  | github.com/spf13/cobra.(*Command).ExecuteC(0xc000b24000)
otc-otc-1  |    github.com/spf13/cobra@v1.7.0/command.go:1068 +0x3a5
otc-otc-1  | github.com/spf13/cobra.(*Command).Execute(0xc0006eb110?)
otc-otc-1  |    github.com/spf13/cobra@v1.7.0/command.go:992 +0x13
otc-otc-1  | main.runInteractive({{0xc0006eb110, 0xc000b200c0, 0xc0006eb200, 0xc0006eb0e0, 0xc000b200f0}, {{0x436fd4c, 0xa}, {0x43d9ac3, 0x24}, {0x436598d, ...}}, ...})
otc-otc-1  |    go.opentelemetry.io/collector/cmd/builder/main.go:31 +0x45
otc-otc-1  | main.run(...)
otc-otc-1  |    go.opentelemetry.io/collector/cmd/builder/main_others.go:11
otc-otc-1  | main.main()
otc-otc-1  |    go.opentelemetry.io/collector/cmd/builder/main.go:24 +0x1d8

Testing:

• Added unit test
• Tested by setting up a directory w/file_storage extension that did not have the necessary permissions.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Files	Coverage Δ
...porter/exporterhelper/internal/persistent_queue.go	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

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