[gimp/gimp-2-10] Issue #1783 - Xcf file crashing gimp-console-2.10 ...

[Ell <ell src gnome org>]

commit d5e1af7d52a6c155cc5532406ec494aad84ba564
Author: Ell <ell_se yahoo com>
Date:   Thu Jul 5 20:19:40 2018 -0400

    Issue #1783 - Xcf file crashing gimp-console-2.10 ...
    
    ... (Invalid read reported by valgrind)
    
    In xcf_read_int8(), avoid calling g_input_stream_read_all() with
    data == NULL and count == 0, in which case it raises a CRITICAL and
    doesn't set bytes_read, which we proceed to use uninitialized.
    This can happen, e.g., when reading an empty parasite.
    
    (cherry picked from commit 6ebadea7c142c9601d96254ae2ddded521b1065d)

 app/xcf/xcf-read.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)
---
diff --git a/app/xcf/xcf-read.c b/app/xcf/xcf-read.c
index 420da7040f..2c281a87bf 100644
--- a/app/xcf/xcf-read.c
+++ b/app/xcf/xcf-read.c
@@ -37,12 +37,18 @@ xcf_read_int8 (XcfInfo *info,
                guint8  *data,
                gint     count)
 {
-  gsize bytes_read;
+  gsize bytes_read = 0;
 
-  g_input_stream_read_all (info->input, data, count,
-                           &bytes_read, NULL, NULL);
+  /* we allow for 'data == NULL && count == 0', which g_input_stream_read_all()
+   * rejects.
+   */
+  if (count > 0)
+    {
+      g_input_stream_read_all (info->input, data, count,
+                               &bytes_read, NULL, NULL);
 
-  info->cp += bytes_read;
+      info->cp += bytes_read;
+    }
 
   return bytes_read;
 }