Fix a problem with loading Qt's translation files

Add this to your merge proposal:
--------------------------------
lp:~raoul-snyman/openlp/fix-translations-2.4 (revision 2680)
[SUCCESS] https://ci.openlp.io/job/Branch-01-Pull/1943/
[SUCCESS] https://ci.openlp.io/job/Branch-02-Functional-Tests/1854/
[SUCCESS] https://ci.openlp.io/job/Branch-03-Interface-Tests/1795/
[SUCCESS] https://ci.openlp.io/job/Branch-04a-Windows_Functional_Tests/1521/
[SUCCESS] https://ci.openlp.io/job/Branch-04b-Windo...