Fix NPE crash when uploading files

Fixes #9099

src/main/java/com/owncloud/android/ui/activity/FileDisplayActivity.java

@@ -949,7 +949,7 @@ public class FileDisplayActivity extends FileActivity
     }
 
     private void requestUploadOfFilesFromFileSystem(String localBasePath, String[] filePaths, int resultCode) {
-        if (filePaths != null) {
+        if (localBasePath != null && filePaths != null) {
             if (!localBasePath.endsWith("/")) {
                 localBasePath = localBasePath + "/";
             }