Fix bug in qasm parser when gates.U3 is present.

[renatomello]

Checklist:

• Reviewers confirm new code works as expected.
• Tests are passing.
• Coverage does not decrease.
• Documentation is updated.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.67%. Comparing base (2e0450b) to head (e02cf4d).
Report is 22 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1555   +/-   ##
=======================================
  Coverage   99.67%   99.67%           
=======================================
  Files          76       76           
  Lines       11234    11236    +2     
=======================================
+ Hits        11198    11200    +2     
  Misses         36       36           

Flag	Coverage Δ
unittests	99.67% <100.00%> (+<0.01%)	⬆️

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