tsbuffer directory: Allow escaping from special://userdata

Kodi's file browser doesn't allow escaping from special://whatever. To
circumvent this, we simply change the default value to empty ("").
In case the user doesn't change the directory, we still set the
original default value in the PVR code.

Fixes #3

pvr.dvbviewer/resources/settings.xml

@@ -21,7 +21,7 @@
   <!-- advanced -->
   <category label="30101">
     <setting label="30020" id="usetimeshift"  type="bool"   default="false" />
-    <setting label="30021" id="timeshiftpath" type="folder" default="special://userdata/addon_data/pvr.dvbviewer" option="writeable" enable="eq(-1,true)" />
+    <setting label="30021" id="timeshiftpath" type="folder" default="" option="writeable" enable="eq(-1,true)" />
 
     <setting id="sep3" type="sep" />
     <setting label="30030" id="usertsp" type="bool" default="false" enable="eq(-3,false)" />

src/client.cpp

@@ -88,7 +88,7 @@ void ADDON_ReadSettings(void)
   if (!XBMC->GetSetting("usetimeshift", &g_useTimeshift))
     g_useTimeshift = false;
 
-  if (XBMC->GetSetting("timeshiftpath", buffer))
+  if (XBMC->GetSetting("timeshiftpath", buffer) && !std::string(buffer).empty())
     g_timeshiftBufferPath = buffer;
 
   if (!XBMC->GetSetting("usertsp", &g_useRTSP) || g_useTimeshift)