[babl] babl: palette, improve assert in pala_to_rgba

[Øyvind "pippin" Kolås <ok src gnome org>]

commit 82aeaea5c3f05a7e3a042305762084d7dc87e408
Author: Øyvind Kolås <pippin gimp org>
Date:   Mon Oct 22 21:41:46 2018 +0200

    babl: palette, improve assert in pala_to_rgba

 babl/babl-palette.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)
---
diff --git a/babl/babl-palette.c b/babl/babl-palette.c
index 9b232ce..205573f 100644
--- a/babl/babl-palette.c
+++ b/babl/babl-palette.c
@@ -448,7 +448,10 @@ pala_to_rgba (Babl *conversion,
               void *src_model_data)
 {
   BablPalette **palptr = src_model_data;
-  BablPalette *pal = *palptr;
+  BablPalette *pal;
+
+  assert(palptr);
+  pal  = *palptr;
 
   assert(pal);
   while (n--)