Fix wrong text shortening in some corner cases ("..." being longer than 2 chars)

[nroggeman-ledger]

Description

The goal of this PR is to fix text shortening (nbgl_textWrapOnNbLines()) in some corner cases ("..." being longer than 2 chars)

Changes include

• Bugfix (non-breaking change that solves an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (change that is not backwards-compatible and/or changes current functionality)
• Tests
• Documentation
• Other (for changes that might not fit in any category)

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 18 lines in your changes missing coverage. Please review.

Project coverage is 35.76%. Comparing base (1acfccd) to head (5d42057).

Files with missing lines	Patch %	Lines
lib_nbgl/src/nbgl_fonts.c	0.00%	18 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #779      +/-   ##
==========================================
+ Coverage   35.67%   35.76%   +0.08%     
==========================================
  Files          13       13              
  Lines        1595     1591       -4     
==========================================
  Hits          569      569              
+ Misses       1026     1022       -4     

Flag	Coverage Δ
unittests	35.76% <0.00%> (+0.08%)	⬆️

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[ndedouhet-ledger]

LGTM