coverity#1340225 Missing break in switch

Change-Id: I9f76340ccdb32f4337d0ebe85e9957fe8a3b19f9
(cherry picked from commit 43e2b417)
Reviewed-on: https://gerrit.libreoffice.org/20176Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

vcl/source/gdi/virdev.cxx

@@ -165,6 +165,7 @@ void VirtualDevice::ImplInitVirDev( const OutputDevice* pOutDev,
     {
         case DeviceFormat::BITMASK:
             mnBitCount = 1;
+            break;
         default:
             mnBitCount = pOutDev->GetBitCount();
             break;