make removable slots only the ones created from editor

src/nodes/base.js

@@ -1245,6 +1245,19 @@
         "number"
     );
 
+    function length(v) {
+        if(v && v.length != null)
+			return Number(v.length);
+		return 0;
+    }
+
+    LiteGraph.wrapFunctionAsNode(
+        "basic/not",
+        function(a){ return !a; },
+        [""],
+        "boolean"
+    );
+
 	function DownloadData() {
         this.size = [60, 30];
         this.addInput("data", 0 );