fix and tests for zero-length arrays in level1 CUBLAS

[kshyatt]

Passing length zero arrays to the mixed element type dot leads to a launch failure right now. Fixed that and added some more tests overall to see that length zero arrays are handled nicely.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.35%. Comparing base (ca67075) to head (179e7c3).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #2994       +/-   ##
===========================================
+ Coverage   76.53%   89.35%   +12.82%     
===========================================
  Files         148      148               
  Lines       12860    12948       +88     
===========================================
+ Hits         9842    11570     +1728     
+ Misses       3018     1378     -1640     

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