ANDROID: Fix setenv error #187

Author: chrisws

src/platform/android/app/src/main/java/net/sourceforge/smallbasic/MainActivity.java

@@ -913,8 +913,8 @@ private final class Storage {
     private final String _media;
 
     private Storage() {
-      String external = null;
-      String media = null;
+      String external = "";
+      String media = "";
 
       String path = Environment.getExternalStorageDirectory().getAbsolutePath();
       if (isPublicStorage(path)) {