6826104: Getting a NullPointer exception when clicked on Application & Toolkit Modal dialog

The addition of window peers to the windows collection has been restored in XWindowPeer.

Reviewed-by: art, dcherepanov
diff --git a/jdk/src/solaris/classes/sun/awt/X11/XWindowPeer.java b/jdk/src/solaris/classes/sun/awt/X11/XWindowPeer.java
index 41807db..d3fb210 100644
--- a/jdk/src/solaris/classes/sun/awt/X11/XWindowPeer.java
+++ b/jdk/src/solaris/classes/sun/awt/X11/XWindowPeer.java
@@ -146,6 +146,13 @@
 
         params.put(OVERRIDE_REDIRECT, Boolean.valueOf(isOverrideRedirect()));
 
+        SunToolkit.awtLock();
+        try {
+            windows.add(this);
+        } finally {
+            SunToolkit.awtUnlock();
+        }
+
         cachedFocusableWindow = isFocusableWindow();
 
         Font f = target.getFont();