Handle early BindingLocalVariablesObject#getMembers for DAP

Author: eregon

src/main/java/org/truffleruby/debug/BindingLocalVariablesObject.java

@@ -48,6 +48,10 @@ protected boolean hasMembers() {
     @ExportMessage
     @TruffleBoundary
     protected Object getMembers(boolean includeInternal) {
+        if (binding == null) { // Not set yet
+            return new VariableNamesObject(StringUtils.EMPTY_STRING_ARRAY);
+        }
+
         String[] variables = BindingNodes.LocalVariablesNode
                 // There should be no duplicates since there is no scope above
                 .listLocalVariablesWithDuplicates(binding.getFrame(), null)