Debugger: Fix LLDB operations with XCode 7.3's lldb-350.0.21.3

The output of lldb changed. Adapt our use.

Task-number: QTCREATORBUG-15965
Task-number: QTCREATORBUG-15945
Task-number: QTCREATORBUG-15949
Change-Id: Ic78593c1a7c4ae69ecf23e381cd2f23441b4829b
Reviewed-by: Christian Stenger <christian.stenger@theqtcompany.com>

share/qtcreator/debugger/dumper.py

@@ -427,6 +427,8 @@ class DumperBase:
 
     # Hex encoding operating on str or bytes, return str.
     def hexencode(self, s):
+        if s is None:
+            s = ''
         if sys.version_info[0] == 2:
             return s.encode("hex")
         if isinstance(s, str):