[Fix] Prob comp in vitstr and parseq for empty words

[felixT2K]

This PR:

• Add 0.0 in prob comp if word is empty

[codecov]

Codecov Report

Merging #1345 (b7bc285) into main (50d65d7) will increase coverage by 0.00%.
Report is 1 commits behind head on main.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1345   +/-   ##
=======================================
  Coverage   95.78%   95.78%           
=======================================
  Files         154      154           
  Lines        6902     6906    +4     
=======================================
+ Hits         6611     6615    +4     
  Misses        291      291           

Flag	Coverage Δ
unittests	95.78% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
...s/detection/differentiable_binarization/pytorch.py	97.77% <100.00%> (ø)
doctr/models/detection/linknet/pytorch.py	98.19% <100.00%> (ø)
doctr/models/recognition/master/pytorch.py	95.53% <100.00%> (+0.04%)	⬆️
doctr/models/recognition/parseq/pytorch.py	97.18% <100.00%> (+0.01%)	⬆️
doctr/models/recognition/parseq/tensorflow.py	97.33% <100.00%> (ø)
doctr/models/recognition/sar/pytorch.py	97.29% <100.00%> (ø)
doctr/models/recognition/vitstr/pytorch.py	100.00% <100.00%> (ø)
doctr/models/recognition/vitstr/tensorflow.py	97.61% <100.00%> (ø)
doctr/models/utils/pytorch.py	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes