fix: shutdown cause concurrent modification

Author: 1zun4

java/org/cef/CefClient.java

@@ -15,6 +15,7 @@
 
 import java.awt.*;
 import java.nio.ByteBuffer;
+import java.util.ArrayList;
 import java.util.Collection;
 import java.util.HashMap;
 import java.util.Vector;
@@ -498,7 +499,7 @@ private void cleanupBrowser(int identifier) {
                 browser_.remove(identifier);
             } else if (!browser_.isEmpty()) {
                 // Close all browsers.
-                Collection<CefBrowser> browserList = browser_.values();
+                Collection<CefBrowser> browserList = new ArrayList<>(browser_.values());
                 for (CefBrowser browser : browserList) {
                     browser.close(true);
                 }