fix(ux): customer portal: disallow empty messages

[ssiyad]

closes #1136

[codecov]

Codecov Report

Patch coverage: 8.33% and project coverage change: -0.06 ⚠️

Comparison is base (b0eab62) 12.86% compared to head (3a3bfef) 12.81%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1143      +/-   ##
==========================================
- Coverage   12.86%   12.81%   -0.06%     
==========================================
  Files          52       52              
  Lines        1803     1811       +8     
==========================================
  Hits          232      232              
- Misses       1571     1579       +8     

Impacted Files	Coverage Δ
...lpdesk/helpdesk/doctype/hd_customer/hd_customer.py	38.09% <0.00%> (-6.35%)	⬇️
...lpdesk/helpdesk/doctype/hd_settings/hd_settings.py	0.00% <0.00%> (ø)
helpdesk/__init__.py	100.00% <100.00%> (ø)

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