Permissions/IO errors can cause nullpointerexception

Fixes arduino#1160

Merge remote-tracking branch 'arduino/master-issue1160'

Author: cmaglie

app/src/processing/app/Base.java

@@ -1179,8 +1179,13 @@ public boolean accept(File dir, String name) {
     Arrays.sort(list, String.CASE_INSENSITIVE_ORDER);
 
     ActionListener listener = new ActionListener() {
-        public void actionPerformed(ActionEvent e) {
-          activeEditor.getSketch().importLibrary(e.getActionCommand());
+        public void actionPerformed(ActionEvent event) {
+          String jarPath = event.getActionCommand();
+          try {
+            activeEditor.getSketch().importLibrary(jarPath);
+          } catch (IOException e) {
+            showWarning(_("Error"), I18n.format("Unable to list header files in {0}", jarPath), e);
+          }
         }
       };
 
@@ -1217,11 +1222,15 @@ public void actionPerformed(ActionEvent e) {
 //        String packages[] =
 //          Compiler.packageListFromClassPath(libraryClassPath);
         libraries.add(subfolder);
+      try {
         String packages[] =
           Compiler.headerListFromIncludePath(subfolder.getAbsolutePath());
         for (String pkg : packages) {
           importToLibraryTable.put(pkg, subfolder);
         }
+      } catch (IOException e) {
+        showWarning(_("Error"), I18n.format("Unable to list header files in {0}", subfolder), e);
+      }
 
         JMenuItem item = new JMenuItem(libraryName);
         item.addActionListener(listener);

app/src/processing/app/Sketch.java

@@ -1128,7 +1128,7 @@ public boolean addFile(File sourceFile) {
    * Add import statements to the current tab for all of packages inside
    * the specified jar file.
    */
-  public void importLibrary(String jarPath) {
+  public void importLibrary(String jarPath) throws IOException {
     // make sure the user didn't hide the sketch folder
     ensureExistence();
 

app/src/processing/app/debug/Compiler.java

@@ -644,14 +644,18 @@ static private void createFolder(File folder) throws RunnerException {
    * not the header files in its sub-folders, as those should be included from
    * within the header files at the top-level).
    */
-  static public String[] headerListFromIncludePath(String path) {
+  static public String[] headerListFromIncludePath(String path) throws IOException {
     FilenameFilter onlyHFiles = new FilenameFilter() {
       public boolean accept(File dir, String name) {
         return name.endsWith(".h");
       }
     };
-    
-    return (new File(path)).list(onlyHFiles);
+
+    String[] list = (new File(path)).list(onlyHFiles);
+    if (list == null) {
+      throw new IOException();
+    }
+    return list;
   }
 
   static public ArrayList<File> findFilesInPath(String path, String extension,