fix[ModVersionListFragment]: Faulty taskProxy logic

Code thought taskProxy was being set to null, when in reality it was
actually just the value of it.

Rather than just read the value of the key, I just delete the key itself
because outside of installing something, we don't need it at all.

Author: alexytomi

app_pojavlauncher/src/main/java/net/kdt/pojavlaunch/fragments/ModVersionListFragment.java

@@ -17,7 +17,6 @@
 import net.kdt.pojavlaunch.R;
 import net.kdt.pojavlaunch.Tools;
 import net.kdt.pojavlaunch.extra.ExtraCore;
-import net.kdt.pojavlaunch.mirrors.DownloadMirror;
 import net.kdt.pojavlaunch.modloaders.ModloaderDownloadListener;
 import net.kdt.pojavlaunch.modloaders.ModloaderListenerProxy;
 import net.kdt.pojavlaunch.progresskeeper.ProgressKeeper;
@@ -106,7 +105,7 @@ public boolean onChildClick(ExpandableListView expandableListView, View view, in
         Object forgeVersion = expandableListView.getExpandableListAdapter().getChild(i, i1);
         ModloaderListenerProxy taskProxy = new ModloaderListenerProxy();
         Runnable downloadTask = createDownloadTask(forgeVersion, taskProxy);
-        setTaskProxy(taskProxy);
+        setTaskProxyValue(taskProxy);
         taskProxy.attachListener(this);
         mExpandableListView.setEnabled(false);
         new Thread(downloadTask).start();
@@ -118,7 +117,7 @@ public void onDownloadFinished(File downloadedFile) {
         Tools.runOnUiThread(()->{
             Context context = requireContext();
             getTaskProxy().detachListener();
-            setTaskProxy(null);
+            deleteTaskProxy();
             mExpandableListView.setEnabled(true);
             // Read the comment in FabricInstallFragment.onDownloadFinished() to see how this works
             getParentFragmentManager().popBackStackImmediate();
@@ -131,7 +130,7 @@ public void onDataNotAvailable() {
         Tools.runOnUiThread(()->{
             Context context = requireContext();
             getTaskProxy().detachListener();
-            setTaskProxy(null);
+            deleteTaskProxy();
             mExpandableListView.setEnabled(true);
             Tools.dialog(context,
                     context.getString(R.string.global_error),
@@ -144,15 +143,18 @@ public void onDownloadError(Exception e) {
         Tools.runOnUiThread(()->{
             Context context = requireContext();
             getTaskProxy().detachListener();
-            setTaskProxy(null);
+            deleteTaskProxy();
             mExpandableListView.setEnabled(true);
             Tools.showError(context, e);
         });
     }
 
-    private void setTaskProxy(ModloaderListenerProxy proxy) {
+    private void setTaskProxyValue(ModloaderListenerProxy proxy) {
         ExtraCore.setValue(mExtraTag, proxy);
     }
+    private void deleteTaskProxy(){
+        ExtraCore.removeValue(mExtraTag);
+    }
 
     private ModloaderListenerProxy getTaskProxy() {
         return (ModloaderListenerProxy) ExtraCore.getValue(mExtraTag);