transcoder: Provide user feedback in options error condition

Remove condition that allows no dialog to be displayed when user selects
options for transcoding. Display the dialog with an error message
instead. This also applies to the transcode options dialog in the
ripping and network remote settings.

src/ripper/ripcddialog.cpp

@@ -187,9 +187,7 @@ void RipCDDialog::Options() {
                                 .value<TranscoderPreset>();
 
   TranscoderOptionsDialog dialog(preset, this);
-  if (dialog.is_valid()) {
-    dialog.exec();
-  }
+  dialog.exec();
 }
 
 // Adds a folder to the destination box.

src/transcoder/transcodedialog.cpp

@@ -314,9 +314,7 @@ void TranscodeDialog::Options() {
                                 .value<TranscoderPreset>();
 
   TranscoderOptionsDialog dialog(preset, this);
-  if (dialog.is_valid()) {
-    dialog.exec();
-  }
+  dialog.exec();
 }
 
 // Adds a folder to the destination box.

src/transcoder/transcoderoptionsdialog.cpp

@@ -56,11 +56,15 @@ TranscoderOptionsDialog::TranscoderOptionsDialog(const TranscoderPreset& preset,
       options_ = new TranscoderOptionsWma(this);
       break;
     default:
+      ui_->errorMessage->setText(
+          tr("Unknown encoder type: %1").arg(preset.name_));
       break;
   }
 
   if (options_) {
-    setWindowTitle(windowTitle() + " - " + Song::TextForFiletype(preset.type_));
+    ui_->errorMessage->setVisible(false);
+    setWindowTitle(tr("Transcoding options - %1")
+                       .arg(Song::TextForFiletype(preset.type_)));
     options_->layout()->setContentsMargins(0, 0, 0, 0);
     ui_->verticalLayout->insertWidget(0, options_);
     resize(width(), minimumHeight());

src/transcoder/transcoderoptionsdialog.h

@@ -33,8 +33,6 @@ class TranscoderOptionsDialog : public QDialog {
                           QWidget* parent = nullptr);
   ~TranscoderOptionsDialog();
 
-  bool is_valid() const { return options_; }
-
   void accept();
 
   void set_settings_postfix(const QString& settings_postfix);

src/transcoder/transcoderoptionsdialog.ui

@@ -14,6 +14,19 @@
    <string>Transcoding options</string>
   </property>
   <layout class="QVBoxLayout" name="verticalLayout">
+   <item>
+    <widget class="QLabel" name="errorMessage">
+     <property name="enabled">
+      <bool>true</bool>
+     </property>
+     <property name="text">
+      <string>Error</string>
+     </property>
+     <property name="alignment">
+      <set>Qt::AlignLeading|Qt::AlignLeft|Qt::AlignTop</set>
+     </property>
+    </widget>
+   </item>
    <item>
     <widget class="QDialogButtonBox" name="buttonBox">
      <property name="orientation">

src/ui/networkremotesettingspage.cpp

@@ -206,7 +206,5 @@ void NetworkRemoteSettingsPage::Options() {
 
   TranscoderOptionsDialog dialog(preset, this);
   dialog.set_settings_postfix(NetworkRemote::kTranscoderSettingPostfix);
-  if (dialog.is_valid()) {
-    dialog.exec();
-  }
+  dialog.exec();
 }