graceful error for dropping folder into sketch window (fixes #441)

Author: benfry

app/src/processing/app/Sketch.java

@@ -1409,6 +1409,11 @@ public void handleAddFile() {
    * @return true if successful.
    */
   public boolean addFile(File sourceFile) {
+    if (sourceFile.isDirectory()) {
+      System.err.println("Skipping folder " + sourceFile);
+      System.err.println("Dragging and dropping a folder is not supported.");
+      return false;
+    }
     String filename = sourceFile.getName();
     File destFile = null;
     String codeExtension = null;

todo.txt

@@ -2,10 +2,8 @@
 X fix logic for opening the correct 'main' tab in handleOpen()
 X   opening AspectHelper.js makes it the main tab
 X   through sketch.properties is not rewritten
-
-
-_ dropping folder into sketch window throws weird exception
-_   https://github.com/processing/processing4/issues/441
+X dropping folder into sketch window throws weird exception
+X   https://github.com/processing/processing4/issues/441
 
 _ clicking "Update All" on the Updates tab throws NPE
 _   https://github.com/processing/processing4/issues/440