Fix compilation with Qt 5.12 and Qt 5.13
Despite Qt 5.12 being the minimum required Qt version, the following functions introduced in Qt 5.14 were used:
- QComboBox::textActivated (in settings/konqhtml/appearance.cpp)
- downloadFileName, downloadDirectory, setDownloadFileName, setDownloadDirectory in QWebEngineDownloadItem
Don't use QComboBox::textActivated
Use QWebEngineDownloadItem::path and QWebEngineDownloadItem::setPath with Qt 5.13