fix(mixpanel incremental properties): add check for undefined properties

[Gauravudia]

Description of the change

Add null/undefined safety check for properties.

Type of change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Related issues

Fix #1

Checklists

Development

• Lint rules pass locally
• The code changed/added as part of this pull request has been covered with tests
• All tests related to the changed code pass in development

Code review

• This pull request has a descriptive title and information useful to a reviewer. There may be a screenshot or screencast attached
• "Ready for review" label attached to the PR and reviewers mentioned in a comment
• Changes have been reviewed by at least one other engineer
• Issue from task tracker has a link to this pull request

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (22dc7b8) 86.89% compared to head (a7a925b) 86.89%.

Additional details and impacted files

@@               Coverage Diff                @@
##           release/v1.42.0    #2634   +/-   ##
================================================
  Coverage            86.89%   86.89%           
================================================
  Files                  603      603           
  Lines                28140    28141    +1     
  Branches              6697     6698    +1     
================================================
+ Hits                 24451    24452    +1     
  Misses                3356     3356           
  Partials               333      333           

Files Changed	Coverage Δ
src/v0/destinations/mp/transform.js	97.37% <100.00%> (+<0.01%)	⬆️

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[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

68.5% Coverage
0.0% Duplication