Same as fdo#67615 for TexFields, but for ComboBox.
Same problem, same cause, same solution.
ListBox seems not to have this problem :)

Change-Id: I953c5452f6c313b8940fbd1048b4c901b331fc58
Reviewed-on: https://gerrit.libreoffice.org/13578Reviewed-by: Lionel Elie Mamane <lionel@mamane.lu>
Tested-by: Lionel Elie Mamane <lionel@mamane.lu>