Make sure clipboard uses \n line endings

This is required by the protocol so we should make sure it is
enforced. We are tolerant of clients that violate this though and
convert incoming clipboard data.
diff --git a/vncviewer/Viewport.cxx b/vncviewer/Viewport.cxx
index 5df5c79..15a3ec4 100644
--- a/vncviewer/Viewport.cxx
+++ b/vncviewer/Viewport.cxx
@@ -1,5 +1,5 @@
 /* Copyright (C) 2002-2005 RealVNC Ltd.  All Rights Reserved.
- * Copyright 2011-2014 Pierre Ossman for Cendio AB
+ * Copyright 2011-2019 Pierre Ossman for Cendio AB
  * 
  * This is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -549,7 +549,7 @@
 
 int Viewport::handle(int event)
 {
-  char *buffer;
+  char *buffer, *filtered;
   int ret;
   int buttonMask, wheelMask;
   DownMap::const_iterator iter;
@@ -564,22 +564,26 @@
     ret = fl_utf8toa(Fl::event_text(), Fl::event_length(), buffer,
                      Fl::event_length() + 1);
     assert(ret < (Fl::event_length() + 1));
+    filtered = convertLF(buffer, ret);
+    delete [] buffer;
 
     if (!hasFocus()) {
-      pendingClientCutText = buffer;
+      pendingClientCutText = new char[strlen(filtered) + 1];
+      strcpy((char*)pendingClientCutText, filtered);
+      strFree(filtered);
       return 1;
     }
 
-    vlog.debug("Sending clipboard data (%d bytes)", (int)strlen(buffer));
+    vlog.debug("Sending clipboard data (%d bytes)", (int)strlen(filtered));
 
     try {
-      cc->writer()->writeClientCutText(buffer, ret);
+      cc->writer()->writeClientCutText(filtered, strlen(filtered));
     } catch (rdr::Exception& e) {
       vlog.error("%s", e.str());
       exit_vncviewer(e.str());
     }
 
-    delete [] buffer;
+    strFree(filtered);
 
     return 1;