Exit if zeronet is not installed

src/freedombone-mesh

@@ -379,6 +379,10 @@ if [ ! $peer_index ]; then
 fi
 
 if [[ $peer_index == 1 ]]; then
+    if [ ! -d $ZERONET_DIR ]; then
+        echo 'zeronet was not installed'
+        exit 63
+    fi
     cd $ZERONET_DIR
 
     if [ ! -d ~/.bttrack ]; then