Clean up internal clipboard handling

We now filter incoming data, which means we can start assuming the
clipboard data is always null terminated. This allows us to clean
up a lot of the internal handling.
diff --git a/common/rfb/SMsgReader.cxx b/common/rfb/SMsgReader.cxx
index 0c0e8b2..5efbfe2 100644
--- a/common/rfb/SMsgReader.cxx
+++ b/common/rfb/SMsgReader.cxx
@@ -215,7 +215,7 @@
   CharArray ca(len);
   is->readBytes(ca.buf, len);
   CharArray filtered(convertLF(ca.buf, len));
-  handler->clientCutText(filtered.buf, strlen(filtered.buf));
+  handler->clientCutText(filtered.buf);
 }
 
 void SMsgReader::readQEMUMessage()