patches/SourceCodeEditorZMI: allow edition without getPreferredSourceCodeEditorKeymap

on (very) old ERP5 instances this does not exist, so when something is
wrong we can not edit python scripts
Status Job ID Name Coverage
  External
failed ERP5.CodingStyleTest-TestRunner2

01:22:47

passed ERP5.UnitTest-TestRunner2

01:29:42

failed ERP5.UnitTest-TestRunner2

01:44:57

canceled ERP5.UnitTest-TestRunner2