Adds some backup fixes

Fixes a potential NullPointerException
Adds a check to make sure the backup location has enough available space
Adds a message when calculating backup size to make it clear that the software is not frozen

src/main/java/net/knarcraft/minecraftserverlauncher/userinterface/BackupGUI.java

@@ -64,12 +64,13 @@ public class BackupGUI implements ActionListener {
      * @param progressPercent <p>The new percent of the progress bar</p>
      */
     public static void updateProgress(String infoText, int progressPercent) {
-        if (progressTextArea == null || progressBar == null) {
-            return;
-        }
+        if (progressTextArea != null) {
             progressTextArea.setText(infoText);
+        }
+        if (progressBar != null) {
             progressBar.setValue(progressPercent);
         }
+    }
 
     /**
      * Destroys the backup GUI

src/main/java/net/knarcraft/minecraftserverlauncher/utility/BackupUtil.java

@@ -114,11 +114,20 @@ public class BackupUtil {
         }
 
         gui.setStatus("Backup running...");
-
         List<List<File>> serverFolders = getFoldersOfEnabledServers(path);
 
+        gui.setStatus("Calculating backup size...");
         long backupFileSize = getFolderSize(gui, serverFolders);
 
+        long locationFreeSpace = path.getFreeSpace();
+        if (locationFreeSpace < (backupFileSize + 2048000000)) {
+            gui.setStatus("Not enough available space. " + (backupFileSize / 1000000) + "MB necessary, but only " +
+                    (locationFreeSpace / 1000000) + "MB available");
+            backupRunning = false;
+            backupAborted = true;
+            return;
+        }
+
         gui.setStatus("Backing up " + (backupFileSize / 1000000) + "MB");
 
         performBackup(gui, serverFolders, backupFileSize);