[gimp] app: handle GIMP_ZOOM_SMOOTH in gimp_palette_editor_zoom()

[Michael Natterer <mitch src gnome org>]

commit 38ef1054d17e7e900c51a79ade34865c8967b232
Author: Michael Natterer <mitch gimp org>
Date:   Wed May 23 12:41:46 2018 +0200

    app: handle GIMP_ZOOM_SMOOTH in gimp_palette_editor_zoom()

 app/widgets/gimppaletteeditor.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/app/widgets/gimppaletteeditor.c b/app/widgets/gimppaletteeditor.c
index 2fcc3d1..96b0917 100644
--- a/app/widgets/gimppaletteeditor.c
+++ b/app/widgets/gimppaletteeditor.c
@@ -540,6 +540,9 @@ gimp_palette_editor_zoom (GimpPaletteEditor  *editor,
                        (gdouble) rows - SPACING) / ENTRY_HEIGHT;
       }
       break;
+
+    case GIMP_ZOOM_SMOOTH: /* can't happen */
+      g_return_if_reached ();
     }
 
   zoom_factor = CLAMP (zoom_factor, 0.1, 4.0);