cloud-init analyze show - IndexError: pop from empty list

This bug was originally filed in Launchpad as [LP: #1799511](https://bugs.launchpad.net/cloud-init/+bug/1799511)

Launchpad details

affected_projects = []

assignee = None

assignee_name = None

date_closed = None

date_created = 2018-10-23T16:31:08.733994+00:00

date_fix_committed = None

date_fix_released = None

id = 1799511

importance = medium

is_complete = False

lp_url = https://bugs.launchpad.net/cloud-init/+bug/1799511

milestone = None

owner = philroche

owner_name = Philip Roche

private = False

status = confirmed

submitter = philroche

submitter_name = Philip Roche

tags = ['id-5baa9659e21d6e6664eaed37']

duplicates = []

_Launchpad user **Philip Roche(philroche)** wrote on 2018-10-23T16:31:08.733994+00:00_

When testing a new 18.10 minimal image on Azure I was gathering boot speed data and ran into the following error when trying to run `cloud-init analyze show` or `cloud-init analyze blame`. `cloud-init analyze dump` did not raise an exception.

The cloud-init version in use is cloud-init 18.4-7-g4652b196-0ubuntu1

'''
Traceback (most recent call last):
File "/usr/bin/cloud-init", line 11, in
load_entry_point('cloud-init==18.4', 'console_scripts', 'cloud-init')()
File "/usr/lib/python3/dist-packages/cloudinit/cmd/main.py", line 904, in main
get_uptime=True, func=functor, args=(name, args))
File "/usr/lib/python3/dist-packages/cloudinit/util.py", line 2519, in log_time
ret = func(*args, **kwargs)
File "/usr/lib/python3/dist-packages/cloudinit/analyze/__main__.py", line 104, in analyze_show
args.print_format)):
File "/usr/lib/python3/dist-packages/cloudinit/analyze/show.py", line 192, in show_events
return generate_records(events, print_format=print_format)
File "/usr/lib/python3/dist-packages/cloudinit/analyze/show.py", line 175, in generate_records
prev_evt = unprocessed.pop()
IndexError: pop from empty list
'''

I have attached the archive from `sudo cloud-init collect-logs`

Start in cloudinit/analyze/show.py at generate_records, where the traceback shows the empty-list pop, and reproduce with cloud-init analyze show or cloud-init analyze blame using the attached collected logs. Done means both commands process the reported data without raising IndexError, while analyze dump continues to work.

Written by the indexing model from the issue text.