[niepce] Build with -Wnon-virtual-dtor

[Hubert Figuière <hub src gnome org>]

commit 6bf9553723ef77a8dc76b1b3b2c89b126ad61c71
Author: Hubert Figuière <hub figuiere net>
Date:   Tue Sep 27 23:15:57 2022 -0400

    Build with -Wnon-virtual-dtor

 configure.ac                 | 1 +
 src/fwk/toolkit/uiresult.hpp | 1 +
 2 files changed, 2 insertions(+)
---
diff --git a/configure.ac b/configure.ac
index f60c614c..eaa8a3c0 100644
--- a/configure.ac
+++ b/configure.ac
@@ -105,6 +105,7 @@ dnl sigc++ 2.10.0 breaks with that warning.
    -Wlogical-not-parentheses \
    -Wmisleading-indentation \
    -Wmissing-noreturn \
+   -Wnon-virtual-dtor \
    -Woverloaded-virtual \
 dnl Gtk+ 3.22.30 breaks with that warning
    -Wno-parentheses \
diff --git a/src/fwk/toolkit/uiresult.hpp b/src/fwk/toolkit/uiresult.hpp
index e157ccc5..4c60e30c 100644
--- a/src/fwk/toolkit/uiresult.hpp
+++ b/src/fwk/toolkit/uiresult.hpp
@@ -33,6 +33,7 @@ namespace fwk {
 class UIResult
 {
 public:
+    virtual ~UIResult() {}
     virtual void clear() = 0;
 
     sigc::connection connect(sigc::slot<void()> slot) {