Improve QML code quality

[HenkKalkwater]

Here is a list of warnings currently emitted by QML and general improvements to make:

• Handle undefined values properly:

  • harbour-sailfin/sailfish/qml/components/ItemChildrenShowcase.qml

    Line 50 in 57b6729

    value: model.imageBlurHashes["Primary"][model.imageTags["Primary"]]

    
    Generates messages like TypeError: Cannot read property 'undefined' of undefined and TypeError: Cannot read property '255dd5b642ae62e684b41d3f0a32c3d6' of undefined

  • harbour-sailfin/sailfish/qml/pages/itemdetails/FilmPage.qml

    Line 31 in 57b6729

    imageBlurhash: itemData.imageBlurHashes["Backdrop"][itemData.backdropImageTags[0]]

  • harbour-sailfin/sailfish/qml/pages/itemdetails/VideoPage.qml

    Line 41 in 57b6729

    property string imageBlurhash: itemData.imageBlurHashes["Primary"][itemData.imageTags["Primary"]]

  • harbour-sailfin/sailfish/qml/pages/itemdetails/MusicArtistPage.qml

    Line 113 in 57b6729

    blurhash: itemData.imageBlurHashes["Backdrop"][itemData.backdropImageTags[0]]

  • harbour-sailfin/sailfish/qml/pages/itemdetails/MusicArtistPage.qml

    Line 135 in 57b6729

    blurhash: itemData.imageBlurHashes["Primary"][itemData.imageTags["Primary"]]

• Fix up some nonsensical conditionals and code

  • harbour-sailfin/sailfish/qml/cover/CollectionPage.qml

    Line 35 in 57b6729

    readonly property bool hasParent: !appWindow.itemData !== null && appWindow.itemData.jellyfinId.length !== 0

  • harbour-sailfin/sailfish/qml/harbour-sailfin.qml

    Line 197 in 57b6729

    pageStack.replace(pages)

  • harbour-sailfin/sailfish/qml/components/ItemChildrenShowcase.qml

    Line 53 in 57b6729

    progress: (typeof model.userDataPlayedProgress !== 0.0) ? model.userDataPlayedPercentage / 100 : 0.0

• Use the Binding element with the when property instead of assigning Qt.binding() values in scripts

  • harbour-sailfin/sailfish/qml/pages/itemdetails/BaseDetailPage.qml

    Line 107 in 57b6729

    appWindow.itemData = Qt.binding(function() { return jItemLoader.data; })

  • harbour-sailfin/sailfish/qml/pages/itemdetails/MusicAlbumPage.qml

    Lines 105 to 111 in 57b6729

    	item.albumArt = Qt.binding(function(){ return Utils.itemImageUrl(apiClient.baseUrl, itemData, "Primary", {"maxWidth": parent.width})})
    	item.name = Qt.binding(function(){ return itemData.name})
    	item.listview = Qt.binding(function() { return list})
    	item.aspectRatio = Qt.binding(function() { return itemData.primaryImageAspectRatio})
    	item.blurhash = Qt.binding(function() { return itemData.imageBlurHashes["Primary"][itemData.imageTags["Primary"]]; })
    	item.twoColumns = Qt.binding(function() { return _twoColumns })
    	item.description = Qt.binding(function() { return _description })