Fix crash when receiving a message that wants an ack on a closed exchange that's still alive.

[bzbarsky-apple]

The basic scenario, with all messages requesting acks, is:

1. A sends message to B.
2. B responds to A, piggybacks ack, closes exchange.
3. A responds to B, piggybacks ack.

When B receives the message, the exchange is still alive, waiting for
an ack. It gets the message handed to it, processes it, queues up an
ack for the message it just got. Then the stack unwinds, the
exchange's refcount drops to 0 (because it's no longer waiting for an
ack, so not referenced by the reliable message manager), and its
destructor tries to flush the pending ack, which fails assertions due
to the refcount being 0.

The fix is to always immediately send a standalone ack if we
have no delegate, because in that situation there won't be anything
app-level to piggyback on.

Problem

Crash on receiving a message. To reproduce easily:

1. scripts/examples/gn_build_example.sh examples/all-clusters-app/linux out/debug/standalone chip_config_network_layer_ble=false
2. scripts/examples/gn_build_example.sh examples/chip-tool out/debug/standalone/
3. In terminal 1: ./out/debug/standalone/chip-all-clusters-app
4. In terminal 2:

   out/debug/standalone/chip-tool pairing onnetwork 0 20202021 3840 ::1 11097
   ./out/debug/standalone/chip-tool onoff report on-off 1 2 3
   

Change overview

Fix the crash by immediately flushing out the pending ack if we have no delegate (which includes when we're closed), so that we don't try to do it from our destructor.

Testing

Unit test added in the PR. Manually tested the steps above.

[github-actions]

Size increase report for "esp32-example-build" from 8551b50

File	Section	File	VM
chip-shell.elf	.flash.text	36	36
chip-all-clusters-app.elf	.flash.text	36	36
chip-temperature-measurement-app.elf	.flash.text	36	36
chip-lock-app.elf	.flash.text	36	36

Full report output

BLOAT REPORT

Files found only in the build output:
    report.csv

Comparing ./master_artifact/chip-pigweed-app.elf and ./pull_artifact/chip-pigweed-app.elf:

sections,vmsize,filesize

Comparing ./master_artifact/chip-shell.elf and ./pull_artifact/chip-shell.elf:

sections,vmsize,filesize
.debug_loc,0,166
.debug_line,0,102
.debug_info,0,62
.flash.text,36,36
.debug_ranges,0,16
.debug_str,0,2

Comparing ./master_artifact/chip-all-clusters-app.elf and ./pull_artifact/chip-all-clusters-app.elf:

sections,vmsize,filesize
.debug_loc,0,166
.debug_line,0,102
.debug_info,0,62
.flash.text,36,36
.debug_ranges,0,16
.debug_str,0,-2

Comparing ./master_artifact/chip-temperature-measurement-app.elf and ./pull_artifact/chip-temperature-measurement-app.elf:

sections,vmsize,filesize
.debug_line,0,84
.debug_info,0,66
.flash.text,36,36
.debug_loc,0,-46

Comparing ./master_artifact/chip-persistent-storage.elf and ./pull_artifact/chip-persistent-storage.elf:

sections,vmsize,filesize

Comparing ./master_artifact/chip-lock-app.elf and ./pull_artifact/chip-lock-app.elf:

sections,vmsize,filesize
.debug_loc,0,166
.debug_line,0,102
.debug_info,0,62
.flash.text,36,36
.debug_ranges,0,16
.debug_str,0,2

[github-actions]

Size increase report for "nrfconnect-example-build" from 8551b50

File	Section	File	VM
chip-shell.elf	text	36	36
chip-shell.elf	device_handles	-4	-4
chip-lock.elf	text	36	36
chip-lock.elf	device_handles	-4	-4

Full report output

BLOAT REPORT

Files found only in the build output:
    report.csv

Comparing ./master_artifact/chip-shell.elf and ./pull_artifact/chip-shell.elf:

sections,vmsize,filesize
.debug_info,0,60
.debug_loc,0,52
.debug_line,0,40
text,36,36
device_handles,-4,-4

Comparing ./master_artifact/chip-lock.elf and ./pull_artifact/chip-lock.elf:

sections,vmsize,filesize
.debug_info,0,60
.debug_loc,0,52
.debug_line,0,40
text,36,36
device_handles,-4,-4

[github-actions]

Size increase report for "gn_qpg6100-example-build" from 8551b50

File	Section	File	VM
chip-qpg6100-lighting-example.out	.text	32	32

Full report output

BLOAT REPORT

Files found only in the build output:
    report.csv

Comparing ./master_artifact/chip-qpg6100-lighting-example.out.map and ./pull_artifact/chip-qpg6100-lighting-example.out.map:

BLOAT EXECUTION FAILED WITH CODE 1:
bloaty: unknown file type for file './pull_artifact/chip-qpg6100-lighting-example.out.map'

Comparing ./master_artifact/chip-qpg6100-lighting-example.out and ./pull_artifact/chip-qpg6100-lighting-example.out:

sections,vmsize,filesize
.debug_info,0,60
.debug_loc,0,54
.debug_line,0,39
.text,32,32
.debug_str,0,-1
[Unmapped],0,-32

[woody-apple]

@mspang @LuDuda ?

[woody-apple]

@Damian-Nordic ?