cygwin: Remove comparison of 'this' to 'NULL' in _pinfo::root

Fix all callers.

winsup/cygwin/fhandler_process.cc

@@ -478,7 +478,7 @@ format_process_root (void *data, char *&destbuf)
       cfree (destbuf);
       destbuf = NULL;
     }
-  destbuf = p->root (fs);
+  destbuf = p ? p->root (fs) : NULL;
   if (!destbuf || !*destbuf)
     {
       destbuf = cstrdup ("<defunct>");

winsup/cygwin/pinfo.cc

@@ -884,7 +884,7 @@ char *
 _pinfo::root (size_t& n)
 {
   char *s;
-  if (!this || !pid)
+  if (!pid)
     return NULL;
   if (pid != myself->pid && !ISSTATE (this, PID_NOTCYGWIN))
     {