updates on start.sh file

typo correction on env variable: replacing $USER with $NB_USER since $USER is not set
test if group exists before trying to add a new group

base-notebook/start.sh

@@ -77,11 +77,13 @@ if [ $(id -u) == 0 ] ; then
     fi
 
     # Change UID:GID of NB_USER to NB_UID:NB_GID if it does not match
-    if [ "$NB_UID" != $(id -u $NB_USER) ] || [ "$NB_GID" != $(id -g $NB_USER) ] ; then
+    if [ "$NB_UID" != $(id -u $NB_USER) ] || [ "$NB_GID" != $(id -g $NB_USER) ]; then
         echo "Set user $NB_USER UID:GID to: $NB_UID:$NB_GID"
+        if [ "$NB_GID" != $(id -g $NB_USER) ]; then
+            groupadd -g $NB_GID -o ${NB_GROUP:-${NB_USER}}
+        fi
         userdel $NB_USER
-        groupadd -g $NB_GID -o ${NB_GROUP:-${NB_USER}}
-        useradd --home /home/$USER -u $NB_UID -g $NB_GID -G 100 -l $NB_USER
+        useradd --home /home/$NB_USER -u $NB_UID -g $NB_GID -G 100 -l $NB_USER
     fi
 
     # Enable sudo if requested