Extract isDownloading check into method of status class.

This is also going to be used elsewhere.

app/src/main/java/org/fdroid/fdroid/AppDetails2.java

@@ -691,8 +691,7 @@ public class AppDetails2 extends AppCompatActivity implements ShareChooserDialog
 
     @Override
     public boolean isAppDownloading() {
-        return currentStatus != null &&
-                (currentStatus.status == AppUpdateStatusManager.Status.PendingDownload || currentStatus.status == AppUpdateStatusManager.Status.Downloading);
+        return currentStatus != null && currentStatus.isDownloading();
     }
 
     @Override

app/src/main/java/org/fdroid/fdroid/AppUpdateStatusManager.java

@@ -184,6 +184,10 @@ public final class AppUpdateStatusManager {
             copy.progressMax = progressMax;
             return copy;
         }
+
+        public boolean isDownloading() {
+            return status == Status.Downloading || status == Status.PendingDownload;
+        }
     }
 
     private final Context context;