Fix filename substitution in shader error reporting for first included file

panda/src/gobj/shader.I

@@ -865,7 +865,7 @@ get_filename_from_index(int index, ShaderType type) const {
     if (!fn.empty()) {
       return fn;
     }
-  } else if (glsl_preprocess && index > 2048 &&
+  } else if (glsl_preprocess && index >= 2048 &&
              (index - 2048) < (int)_included_files.size()) {
     return _included_files[index - 2048];
   }