Don't change chat width when showing overlay panes

When auto-expanding a pane and showing it as an overlay because of
narrow window, make the chat keep the width it had before.

This makes the transition less jarring, reduces the amount of text seen
through a transparent pane, and fix making one pane overlay expanding
the other.

src/gui/Base/HDrawer.qml

@@ -43,6 +43,11 @@ Drawer {
     property int calculatedMinimumSize:
         requireDefaultSize ? defaultSize : minimumSize
 
+    readonly property int calculatedSizeNoRequiredMinimum:
+        collapse ?
+        peekSizeWhileCollapsed :
+        Math.max(minimumSize, Math.min(preferredSize, maximumSize))
+
     readonly property int calculatedSize:
         collapse ?
         peekSizeWhileCollapsed :

src/gui/Pages/Chat/Chat.qml

@@ -75,14 +75,18 @@ Item {
     HLoader {
         id: loader
         anchors.rightMargin:
-            ready && roomPane &&
+            ! roomPane ?
+            0 :
+
+            ready &&
             ! (
                 roomPane.requireDefaultSize &&
                 roomPane.minimumSize > roomPane.maximumSize &&
                 ! roomPane.collapse
             ) ?
             roomPane.visibleSize :
-            0
+
+            roomPane.calculatedSizeNoRequiredMinimum
 
         anchors.fill: parent
         visible: ! (ready && roomPane && roomPane.visibleSize >= chat.width)

src/gui/UI.qml

@@ -134,7 +134,7 @@ Item {
         anchors.leftMargin:
             mainPane.requireDefaultSize &&
             mainPane.minimumSize > mainPane.maximumSize ?
-            0 :
+            mainPane.calculatedSizeNoRequiredMinimum :
             mainPane.visibleSize
 
         visible: mainPane.visibleSize < mainUI.width