Added a forgotten targetPath (boo#903747).

Respect target root also when the file
does not exist in the original root.

The bug manifested during upgrade of 13.1 to 13.2:
  Internal error. ...
  Caller: /mounts/mp_0001/usr/share/YaST2/modules/Kernel.rb:626:in `block in SaveModulesToLoad'

agent-any/src/AnyAgent.cc

@@ -740,7 +740,7 @@ AnyAgent::readFile (const YCPValue & arg)
     {
         const char *s = ss.c_str();
         // Check modify time if we can use cache
-        if (stat (s, &buf) != 0)
+        if (stat (targetPath(s).c_str(), &buf) != 0)
         {
             mtime = 0;	// error case: reset mtime
             if (errno == ENOENT)