Fix build failure with USE=fltk due to wrong return type.
https://bugs.gentoo.org/627412
--- a/nodeview/path.cc
+++ b/nodeview/path.cc
@@ -47,3 +47,3 @@
     PrintWarn("Unable to open path file: %s\n", strerror(errno));
-    return false;
+    return NULL;
   }