jp (avatar/get): fixed avatar being displayed 2 times in a corner case:

when avatar is shown by ImageMagick's display and it is terminated using SIGINT, the return code is 2 and not 0.
Before this patch, jp was interpreting the 2 as an image not displayed and so was trying with the next available command
Now it is stopping when exit code 2 is received.

sat_frontends/jp/cmd_avatar.py

@@ -88,7 +88,8 @@ class Get(base.CommandBase):
             except OSError:
                 pass
             else:
-                if ret == 0:
+                if ret in (0, 2):
+                    # we can get exit code 2 with display when stopping it with C-c
                     break
         else:
             # didn't worked with commands, we try our luck with webbrowser