Fix issues with VLC

lp:~trb143/openlp/media2018a (revision 2838)
https://ci.openlp.io/job/Branch-01-Pull/2481/                          [SUCCESS]
https://ci.openlp.io/job/Branch-02a-Linux-Tests/2382/                  [SUCCESS]
https://ci.openlp.io/job/Branch-02b-macOS-Tests/169/                   [FAILURE]
https://ci.openlp.io/job/Branch-03a-Build-Source/91/                   [SUCCESS]
https://ci.openlp.io/job/Branch-03b-Build-macOS/84/                    [SUCCESS]
https://ci.openlp.io/job/B...