Fix #134756: Internal text datablock filepath considered missing

When the text datablock was marked as external at one point and the
filepath was allocated, it would be considered missing.

source/blender/blenkernel/intern/text.cc

@@ -155,7 +155,7 @@ static void text_foreach_path(ID *id, BPathForeachPathData *bpath_data)
 {
   Text *text = (Text *)id;
 
-  if (text->filepath != nullptr) {
+  if (text->filepath != nullptr && text->filepath[0] != '\0') {
     BKE_bpath_foreach_path_allocated_process(bpath_data, &text->filepath);
   }
 }