Fixed NullPointerException case on 'Browser' lang selection

Occurred when English was the only active language, then making the
ConfigBasic.html page unusable until manually modifying the
locale.language setting.

source/net/yacy/data/Translator.java

@@ -326,16 +326,23 @@ public class Translator {
      * @return list of language-codes of available/active translations
      */
     public static List<String> activeTranslations() {
-        Switchboard sb = Switchboard.getSwitchboard();
-        File localePath;
-        if (sb != null)
+        final Switchboard sb = Switchboard.getSwitchboard();
+        final File localePath;
+        if (sb != null) {
             localePath = sb.getDataPath("locale.translated_html", "DATA/LOCALE/htroot");
-        else
+        } else {
             localePath = new File ("DATA/LOCALE/htroot");
-        List<String> dirlist = new ArrayList<String>(); // get list of language subdirectories
-        File[] list = localePath.listFiles();
-        for (File f : list) {
-            if (f.isDirectory()) dirlist.add(f.getName()); // filter directories to add to result
+        }
+        final List<String> dirlist = new ArrayList<String>(); // get list of language subdirectories
+        if(localePath.isDirectory()) {
+        	final File[] list = localePath.listFiles();
+        	if(list != null) { // the list may be null on IO error
+        		for (final File f : list) {
+        			if (f.isDirectory()) {
+        				dirlist.add(f.getName()); // filter directories to add to result
+        			}
+        		}
+        	}
         }
         return dirlist;
     }