[Controls] FilterComboBox: Correctly cancel selection or edition

Up until this commit, any action causing the filtering text field to lose
the focus was considered to be a valid edition, thus propagating the value
in the text field or the one highlighted to be propagated, even if the
user was clicking anywhere else in the application, or pressing the
`esc` key.

The distinction is now made between cases where the edition is finished
because it was validated (value clicked on, or selected with the `return`/
`enter` key), and not because it was cancelled (clicks outside of the
combobox or `esc` key pressed).

meshroom/ui/qml/Controls/FilterComboBox.qml

@@ -18,6 +18,7 @@ ComboBox {
 
     property alias filterText: filterTextArea
     property bool validValue: true
+    property string previousText: ""  // Used to restore displayText if the edition is cancelled
 
     enabled: root.editable
     model: {
@@ -73,6 +74,9 @@ ComboBox {
 
         onAboutToShow: {
             filterTextArea.forceActiveFocus()
+            filterTextArea.editingCancelled = true
+
+            previousText = displayText
 
             var dropDown = true
             var posY = mapToGlobal(popup.x, popup.y).y
@@ -101,6 +105,8 @@ ComboBox {
             anchors.fill: parent
             TextArea {
                 id: filterTextArea
+
+                property bool editingCancelled: false
                 leftPadding: 12
                 anchors.left: parent.left
                 anchors.right: parent.right
@@ -114,7 +120,12 @@ ComboBox {
 
                 onEditingFinished: {
                     combo.popup.close()
-                    combo.editingFinished(displayText)
+                    if (editingCancelled) {
+                        displayText = previousText
+                        filterTextArea.clear()
+                    } else {
+                        combo.editingFinished(displayText)
+                    }
                 }
 
                 Keys.onEnterPressed: {
@@ -123,6 +134,7 @@ ComboBox {
                     } else {
                         displayText = currentText
                     }
+                    editingCancelled = false
                     editingFinished()
                 }
 
@@ -132,6 +144,7 @@ ComboBox {
                     } else {
                         displayText = currentText
                     }
+                    editingCancelled = false
                     editingFinished()
                 }
 
@@ -200,4 +213,9 @@ ComboBox {
     onCurrentTextChanged: {
         displayText = currentText
     }
+
+    onActivated: {
+        // This slot is entered when one of the element of the combo is clicked on, causing the popup to close
+        filterTextArea.editingCancelled = false
+    }
 }