[gegl] remap: avoid crashing on unset input pads

[Øyvind Kolås <ok src gnome org>]

commit a7d333edef408166a0d08be55f993e637b5f0077
Author: Øyvind Kolås <pippin gimp org>
Date:   Sun Mar 12 23:24:18 2017 +0100

    remap: avoid crashing on unset input pads

 operations/common/remap.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/operations/common/remap.c b/operations/common/remap.c
index 7b2dd57..edd47aa 100644
--- a/operations/common/remap.c
+++ b/operations/common/remap.c
@@ -57,6 +57,8 @@ process (GeglOperation       *op,
   gfloat *min = min_buf;
   gfloat *max = max_buf;
   gfloat *out = out_buf;
+  if (!min || !max || !out || !in)
+    return FALSE;
 
   for (i = 0; i < n_pixels; i++)
     {