Handle invalid folder locations in callback

This prevents a NullPointerException being thrown when the inputFolder parameter is undefined or invalid during callback

Author: imagejan

src/main/java/org/scijava/batch/FileScriptBatchProcessor.java

@@ -105,6 +105,8 @@ private List<File> populateFileList(File folder, FilenameFilter filter, boolean
 	 * Count all applicable files and display them in the dialog message
 	 */
 	protected void directoryCallback() {
+		if (inputFolder == null || !inputFolder.exists()) return;
+
 		// get list of all applicable files
 		FilenameFilter inputFilter;
 		try {

src/main/java/org/scijava/batch/MenuScriptBatchProcessor.java

@@ -85,6 +85,8 @@ private List<File> populateFileList(File folder, FilenameFilter filter,
 	 * Count all applicable files and display them in the dialog message
 	 */
 	protected void directoryCallback() {
+		if (inputFolder == null || !inputFolder.exists()) return;
+
 		// get list of all applicable files
 		FilenameFilter inputFilter;
 		try {