XAWT: crash when displaying hw combobox popup on secondary screen (sol/lin)

Since it is impossible to reopen the bug(5107634), I filed this one as an absolute copy, see evaluation for reasons.

This is reproducible only on mulriscreen system
(no xinerama), on linux and solaris, with XAWT toolkit only.
It's a regression since 1.4.2, reproducible in both tiger-b64 and mustang-b04.

Run SwingSet2. Create a SS frame on the secondary screen via Multiscreen
menu, go to the Table Demo on the newly created SS frame.

Click the 'Color' cell on the last visible row on the bottom.
Note that the combobox doesn't appear. Click several more
times and java crashes with the following stack trace
(full hs log is attached):
#
# An unexpected error has been detected by HotSpot Virtual Machine:
#
# SIGSEGV (0xb) at pc=0x4dea3b09, pid=1793, tid=98317
#
# Java VM: Java HotSpot(TM) Client VM (1.6.0-ea-b05 mixed mode)
# Problematic frame:
# C [libX11.so.6+0x25b09] XScreenNumberOfScreen+0x9
#
# An error report file with more information is saved as hs_err_pid1793.log
#
# If you would like to submit a bug report, please visit:
# http://java.sun.com/webapps/bugreport/crash.jsp
#
Aborted
Stack: [0x4e225000,0x4e2a5000), sp=0x4e2a4024, free space=508k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
C [libX11.so.6+0x25b09] XScreenNumberOfScreen+0x9
C [libmawt.so+0xd7e7] Java_sun_awt_X11_XlibWrapper_XScreenNumberOfScreen+0x77
j sun.awt.X11.XlibWrapper.XScreenNumberOfScreen(J)J+0
j sun.awt.X11.XBaseWindow.getScreenNumber()J+10
j sun.awt.X11.XBaseWindow.toGlobal(II)Ljava/awt/Point;+11
j sun.awt.X11.XWindow.getLocationOnScreen()Ljava/awt/Point;+93
j java.awt.Component.getLocationOnScreen_NoTreeLock()Ljava/awt/Point;+86
j java.awt.Component.getLocationOnScreen()Ljava/awt/Point;+8
J javax.swing.SwingUtilities.convertPointFromScreen(Ljava/awt/Point;Ljava/awt/Component;)V
v ~RuntimeStub::alignment_frame_return Runtime1 stub
j javax.swing.SwingUtilities.convertPoint(Ljava/awt/Component;Ljava/awt/Point;Ljava/awt/Component;)Ljava/awt/Point;+72
j javax.swing.plaf.basic.BasicComboPopup.convertMouseEvent(Ljava/awt/event/MouseEvent;)Ljava/awt/event/MouseEvent;+15
j javax.swing.plaf.basic.BasicComboPopup$Handler.mouseDragged(Ljava/awt/event/MouseEvent;)V+30
j java.awt.Component.processMouseMotionEvent(Ljava/awt/event/MouseEvent;)V+52
j javax.swing.JComponent.processMouseMotionEvent(Ljava/awt/event/MouseEvent;)V+42
j java.awt.Component.processEvent(Ljava/awt/AWTEvent;)V+92
j java.awt.Container.processEvent(Ljava/awt/AWTEvent;)V+18
j java.awt.Component.dispatchEventImpl(Ljava/awt/AWTEvent;)V+477
j java.awt.Container.dispatchEventImpl(Ljava/awt/AWTEvent;)V+42
J java.awt.LightweightDispatcher.retargetMouseEvent(Ljava/awt/Component;ILjava/awt/event/MouseEvent;)V
j java.awt.LightweightDispatcher.processMouseEvent(Ljava/awt/event/MouseEvent;)Z+191
j java.awt.LightweightDispatcher.dispatchEvent(Ljava/awt/AWTEvent;)Z+50
j java.awt.Container.dispatchEventImpl(Ljava/awt/AWTEvent;)V+12
j java.awt.Window.dispatchEventImpl(Ljava/awt/AWTEvent;)V+19
J java.awt.EventQueue.dispatchEvent(Ljava/awt/AWTEvent;)V
J java.awt.EventDispatchThread.pumpOneEventForHierarchy(ILjava/awt/Component;)Z

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###@###.### 2004-09-29
###@###.### 2004-09-29