erp5_accounting: do not crash if user can not access the source/destination section

bt5/erp5_accounting/SkinTemplateItem/portal_skins/erp5_accounting/AccountingTransaction_isDestinationCurrencyConvertible.py

-section_value = context.getDestinationSectionValue()
+section_value = context.getDestinationSectionValue(checked_permission='Access contents information')
 
 if section_value is None or \
    section_value.getProperty('price_currency', None) is None:

bt5/erp5_accounting/SkinTemplateItem/portal_skins/erp5_accounting/AccountingTransaction_isSourceCurrencyConvertible.py

-section_value = context.getSourceSectionValue()
+section_value = context.getSourceSectionValue(checked_permission='Access contents information')
 
 if section_value is None or \
    section_value.getProperty('price_currency', None) is None: