Fix stack overflow after entity tracker popup has been shown

Failure to load the entity tracker usually (not always) results in
`entityTracker` remaining to be `null`, so there has to be an additional
condition for aborting the thenRun-loadEntityTracker-…-recursion.

src/main/java/com/replaymod/simplepathing/gui/GuiPathing.java

@@ -553,7 +553,7 @@ public class GuiPathing {
     }
 
     public boolean loadEntityTracker(Runnable thenRun) {
-        if (entityTracker == null) {
+        if (entityTracker == null && !errorShown) {
             LOGGER.debug("Entity tracker not yet loaded, delaying...");
             LoadEntityTrackerPopup popup = new LoadEntityTrackerPopup(replayHandler.getOverlay());
             entityTrackerLoadingProgress = p -> popup.progressBar.setProgress(p.floatValue());