AtmManager: Fix memory leaks in tests and apply clang-format

[melvo]

Before opening a pull-request please do:

• [ ] Documentation:
  • [ ] Document every new public class and function
  • [ ] Add \since QXmpp 1.X to newly added classes and functions
  • [ ] Fix any doxygen warnings from your code (see log when building with -DBUILD_DOCUMENTATION=ON)
• [ ] When implementing or updating XEPs add it to doc/xep.doc
• [ ] Add unit tests for everything you've changed or added
• [x] On the top level, run clang-format -i src/<edited-file(s)> tests/<edited-file(s)>

[codecov[bot]]

Codecov Report

Merging #409 (cc12fd1) into master (1a24bd1) will decrease coverage by 0.00%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #409      +/-   ##
==========================================
- Coverage   79.61%   79.60%   -0.01%     
==========================================
  Files         237      237              
  Lines       23920    23911       -9     
==========================================
- Hits        19043    19034       -9     
  Misses       4877     4877              

Impacted Files	Coverage Δ
src/client/QXmppAtmManager.cpp	98.05% <100.00%> (ø)
tests/qxmppatmmanager/tst_qxmppatmmanager.cpp	98.76% <100.00%> (-0.01%)	:arrow_down:

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