8187364: Unable to enter zero width non-joiner (ZWNJ) symbol in Swing text component

Reviewed-by: serb, dmarkov

src/share/classes/javax/swing/text/DefaultEditorKit.java

@@ -878,16 +878,15 @@ public class DefaultEditorKit extends EditorKit {
                         isPrintableMask = ((SunToolkit)tk).isPrintableCharacterModifiersMask(mod);
                     }
 
-                    if (isPrintableMask) {
                     char c = content.charAt(0);
-                        if ((c >= 0x20) && (c != 0x7F)) {
+                    if ((isPrintableMask && (c >= 0x20) && (c != 0x7F)) ||
+                        (!isPrintableMask && (c >= 0x200C) && (c <= 0x200D))) {
                         target.replaceSelection(content);
                     }
                 }
             }
         }
     }
-    }
 
     /**
      * Places content into the associated document.