[babl] extensions: protect gray unpremuls from gggl against division by 0.0

[Øyvind Kolås <ok src gnome org>]

commit 805c7d12ce5cad221551ae4a2801d6297263b5fe
Author: Øyvind Kolås <pippin gimp org>
Date:   Fri Nov 10 10:34:57 2017 +0100

    extensions: protect gray unpremuls from gggl against division by 0.0

 extensions/gggl-lies.c |    5 ++++-
 extensions/gggl.c      |    5 ++++-
 2 files changed, 8 insertions(+), 2 deletions(-)
---
diff --git a/extensions/gggl-lies.c b/extensions/gggl-lies.c
index b34f8ef..c08dccd 100644
--- a/extensions/gggl-lies.c
+++ b/extensions/gggl-lies.c
@@ -356,7 +356,10 @@ conv_gAF_gaF (const Babl *conversion,unsigned char *src, unsigned char *dst, lon
     {
       float alpha = (*(float *) (src + 4));
 
-      *(float *) dst = ((*(float *) src) / alpha);
+      if (alpha == 0.0f)
+        *(float *) dst = 0.0f;
+      else
+        *(float *) dst = ((*(float *) src) / alpha);
       dst           += 4;
       src           += 4;
       *(float *) dst = alpha;
diff --git a/extensions/gggl.c b/extensions/gggl.c
index 83352d2..d101bef 100644
--- a/extensions/gggl.c
+++ b/extensions/gggl.c
@@ -373,7 +373,10 @@ conv_gAF_gaF (const Babl *conversion,unsigned char *src, unsigned char *dst, lon
     {
       float alpha = (*(float *) (src + 4));
 
-      *(float *) dst = ((*(float *) src) / alpha);
+      if (alpha == 0.0f)
+        *(float *) dst = 0.0f;
+      else
+        *(float *) dst = ((*(float *) src) / alpha);
       dst           += 4;
       src           += 4;
       *(float *) dst = alpha;