Bug: When I open the Library Manager, java.util.ConcurrentModificationException gets thrown.

[imrehorvath]

Arduino IDE 1.8.13 on macOS

When I open the Library Manager, I get the below exception thrown sporadically.

Stack-trace:

Exception in thread "AWT-EventQueue-0" java.util.ConcurrentModificationException
	at java.util.ArrayList.sort(ArrayList.java:1464)
	at java.util.Collections.sort(Collections.java:177)
	at cc.arduino.contributions.libraries.ui.LibrariesIndexTableModel.updateContributions(LibrariesIndexTableModel.java:208)
	at cc.arduino.contributions.libraries.ui.LibrariesIndexTableModel.update(LibrariesIndexTableModel.java:138)
	at cc.arduino.contributions.libraries.ui.LibrariesIndexTableModel.updateIndexFilter(LibrariesIndexTableModel.java:60)
	at cc.arduino.contributions.ui.InstallerJDialog.updateIndexFilter(InstallerJDialog.java:293)
	at cc.arduino.contributions.ui.InstallerJDialog$1.onFilter(InstallerJDialog.java:133)
	at cc.arduino.contributions.ui.FilterJTextField.applyFilter(FilterJTextField.java:110)
	at cc.arduino.contributions.ui.FilterJTextField.lambda$new$0(FilterJTextField.java:53)
	at javax.swing.Timer.fireActionPerformed(Timer.java:313)
	at javax.swing.Timer$DoPostEvent.run(Timer.java:245)
	at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:311)
	at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
	at java.awt.EventQueue.access$500(EventQueue.java:97)
	at java.awt.EventQueue$3.run(EventQueue.java:709)
	at java.awt.EventQueue$3.run(EventQueue.java:703)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:74)
	at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
	at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:205)
	at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
	at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:109)
	at java.awt.WaitDispatchSupport$2.run(WaitDispatchSupport.java:190)
	at java.awt.WaitDispatchSupport$4.run(WaitDispatchSupport.java:235)
	at java.awt.WaitDispatchSupport$4.run(WaitDispatchSupport.java:233)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.awt.WaitDispatchSupport.enter(WaitDispatchSupport.java:233)
	at java.awt.Dialog.show(Dialog.java:1084)
	at java.awt.Component.show(Component.java:1671)
	at java.awt.Component.setVisible(Component.java:1623)
	at java.awt.Window.setVisible(Window.java:1014)
	at java.awt.Dialog.setVisible(Dialog.java:1005)
	at processing.app.Base.openLibraryManager(Base.java:1392)
	at processing.app.Base.lambda$rebuildImportMenu$2(Base.java:1117)
	at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
	at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2348)
	at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
	at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
	at javax.swing.AbstractButton.doClick(AbstractButton.java:376)
	at com.apple.laf.ScreenMenuItem.actionPerformed(ScreenMenuItem.java:125)
	at java.awt.MenuItem.processActionEvent(MenuItem.java:669)
	at java.awt.MenuItem.processEvent(MenuItem.java:628)
	at java.awt.MenuComponent.dispatchEventImpl(MenuComponent.java:357)
	at java.awt.MenuComponent.dispatchEvent(MenuComponent.java:345)
	at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:763)
	at java.awt.EventQueue.access$500(EventQueue.java:97)
	at java.awt.EventQueue$3.run(EventQueue.java:709)
	at java.awt.EventQueue$3.run(EventQueue.java:703)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:74)
	at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:84)
	at java.awt.EventQueue$4.run(EventQueue.java:733)
	at java.awt.EventQueue$4.run(EventQueue.java:731)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:74)
	at java.awt.EventQueue.dispatchEvent(EventQueue.java:730)
	at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:205)
	at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
	at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)