[gnumeric] Compilation: kill warning.

[Morten Welinder <mortenw src gnome org>]

commit 940808c624f43ae9fd61898e442b2fe617a6a979
Author: Morten Welinder <terra gnome org>
Date:   Sat Dec 2 16:52:34 2017 -0500

    Compilation: kill warning.
    
    With a g_return_val_if_fail, no complaint about noreturn.

 src/gui-util.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/src/gui-util.c b/src/gui-util.c
index 7ced0af..e6e2820 100644
--- a/src/gui-util.c
+++ b/src/gui-util.c
@@ -1501,6 +1501,7 @@ gnm_style_context_from_selector (GtkStyleContext *parent,
 
   return create_context_for_path (path, parent);
 #else
+  g_return_val_if_fail (selector != NULL, NULL);
   (void)parent;
   (void)selector;
   g_assert_not_reached ();