Add check to make sure tox was created successfully

[e0ff]

This change is 

[codecov]

Codecov Report

Merging #1110 into master will increase coverage by <.1%.
The diff coverage is 100%.

@@           Coverage Diff            @@
##           master   #1110     +/-   ##
========================================
+ Coverage    82.7%   82.7%   +<.1%     
========================================
  Files          80      80             
  Lines       14316   14317      +1     
========================================
+ Hits        11841   11849      +8     
+ Misses       2475    2468      -7

Impacted Files	Coverage Δ
auto_tests/save_compatibility_test.c	88.1% <100%> (+0.2%)	⬆️
auto_tests/set_name_test.c	93.6% <0%> (-6.4%)	⬇️
toxav/toxav.c	68.8% <0%> (-0.7%)	⬇️
toxcore/net_crypto.c	93.7% <0%> (-0.6%)	⬇️
toxcore/Messenger.c	86.2% <0%> (+0.3%)	⬆️
toxav/msi.c	66.7% <0%> (+0.5%)	⬆️
toxcore/tox.c	66.6% <0%> (+0.9%)	⬆️
toxcore/network.c	84.8% <0%> (+1.4%)	⬆️

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[iphydf]

Reviewed 1 of 1 files at r1.
Reviewable status: 0 of 1 approvals obtained