added validation for incoming message (prevents panic)

[kbudde]

Hi,

the problem with of the panic is caused by the embedded pointer to *template.Data in webhook.Message (alertmanager)
https://github.com/prometheus/alertmanager/blob/v0.20.0/notify/webhook/webhook.go#L69

if template.Data is nil, all access to fields of template.Data will cause a panic. For example here:

prometheus-msteams/pkg/card/templated_card.go

Line 60 in 2c78204

Receiver: promAlert.Receiver,

Somewhere the application revers from panic. So maybe you want to keep it like it is?

fixes #209

[codecov-commenter]

Codecov Report

Merging #210 (37f7600) into master (2c78204) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #210   +/-   ##
=======================================
  Coverage   15.80%   15.80%           
=======================================
  Files           5        5           
  Lines         424      424           
=======================================
  Hits           67       67           
  Misses        348      348           
  Partials        9        9           

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[Knappek]

Thanks @kbudde for this PR. Just one minor comment.

[Knappek]

Thanks again @kbudde !