[Bugfix] Don't operate on erased iterator (ID 3112731).


git-svn-id: svn://svn.code.sf.net/p/tigervnc/code/trunk@4204 3789f03b-4d11-0410-bbf8-ca57d06f2519
diff --git a/common/rfb/ScreenSet.h b/common/rfb/ScreenSet.h
index 6f5188c..f2df156 100644
--- a/common/rfb/ScreenSet.h
+++ b/common/rfb/ScreenSet.h
@@ -74,8 +74,9 @@
 
     inline void add_screen(const Screen screen) { screens.push_back(screen); };
     inline void remove_screen(rdr::U32 id) {
-      std::list<Screen>::iterator iter;
-      for (iter = screens.begin();iter != screens.end();++iter) {
+      std::list<Screen>::iterator iter, nextiter;
+      for (iter = screens.begin();iter != screens.end();iter = nextiter) {
+        nextiter = ++iter;
         if (iter->id == id)
             screens.erase(iter);
       }