[FIX] makepot.py - Update the pot file only if odoo generates content

[FrancoMaxime]

In odoo 19 if there is no translatable terms found, instead of creating an empty pot file with an empty line, Odoo return an Empty buffer.

Odoo 18:

# Translation of Odoo Server.
# This file contains the translation of the following modules:
#
msgid ""
msgstr ""
"Project-Id-Version: Odoo Server 18.0+e\n"
"Report-Msgid-Bugs-To: \n"
"Last-Translator: \n"
"Language-Team: \n"
"MIME-Version: 1.0\n"
"Content-Type: text/plain; charset=UTF-8\n"
"Content-Transfer-Encoding: \n"
"Plural-Forms: \n"

Odoo 19:

[codecov-commenter]

Codecov Report

❌ Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 90.73%. Comparing base (7906890) to head (c2c4950).

Files with missing lines	Patch %	Lines
click_odoo_contrib/makepot.py	83.33%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #173      +/-   ##
==========================================
- Coverage   90.83%   90.73%   -0.10%     
==========================================
  Files          14       14              
  Lines         938      939       +1     
  Branches      171      172       +1     
==========================================
  Hits          852      852              
  Misses         55       55              
- Partials       31       32       +1     

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