[gimp] app: fix use of NULL canvas item in iscissors tool

[N/A <ell src gnome org>]

commit 09d6f2bad1b7d846ee44dc4352ec2e6a5d2f18e6
Author: Ell <ell_se yahoo com>
Date:   Sun Jun 11 11:23:52 2017 -0400

    app: fix use of NULL canvas item in iscissors tool
    
    ... when editing an empty segment in interactive mode

 app/tools/gimpiscissorstool.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/app/tools/gimpiscissorstool.c b/app/tools/gimpiscissorstool.c
index a9def3b..e7a7156 100644
--- a/app/tools/gimpiscissorstool.c
+++ b/app/tools/gimpiscissorstool.c
@@ -798,7 +798,8 @@ gimp_iscissors_tool_draw (GimpDrawTool *draw_tool)
                                                 segment->x1, segment->y1,
                                                 segment->x2, segment->y2);
 
-              gimp_canvas_item_set_highlight (item, TRUE);
+              if (item)
+                gimp_canvas_item_set_highlight (item, TRUE);
             }
         }
     }