Fix crash when using MainWindow::layoutEqually()

When distributing space we should honour the other widgets
min-size too, and not give too much

Since the layouting code is complex, this won't be backported to
1.3

tests/test_resources.qrc

@@ -4,6 +4,7 @@
         <file>layouts/overlapping-item.json</file>
         <file>layouts/unsupported-serialization-version.json</file>
         <file>layouts/stuck-separator.json</file>
+        <file>layouts/layoutEquallyCrash.json</file>
         <file>main.qml</file>
     </qresource>
 </RCC>