Set target_since to None when trial failed and animal is not in target

SIT.ipynb

@@ -463,7 +463,7 @@
     "                    islands = []\n",
     "                    phase = 2\n",
     "                    distractor_since = None\n",
-    "                    target_since = None\n",
+    "                    target_since = None # take care of the case in which animal was in target at trial end but exited before target_duration\n",
     "                \n",
     "                else:\n",
     "                    target_since = None\n",