feat(popover): don't show popover if content is undefined, #1504

[LimarenkoDenis]

#1504

PR Checklist

Before creating new PR, please take a look at checklist below to make sure that you've done everything that needs to be done before we can merge it.

• read and followed the CONTRIBUTING.md guide.
• built and tested the changes locally.
• added/updated tests.
• added/updated API documentation.
• added/updated demos.

[codecov]

Codecov Report

Merging #2815 into development will not change coverage.
The diff coverage is 100%.

@@             Coverage Diff              @@
##           development    #2815   +/-   ##
============================================
  Coverage        70.44%   70.44%           
============================================
  Files              137      137           
  Lines             4094     4094           
  Branches           712      712           
============================================
  Hits              2884     2884           
  Misses             912      912           
  Partials           298      298

Impacted Files	Coverage Δ
src/popover/popover.directive.ts	80% <100%> (ø)	⬆️

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[YevheniiaMazur]

Tested, looks good