Fix some bug:

Avoid dismiss dialog already dismissed
Avoid access to invalid index when have no server

app/src/main/java/fr/mobdev/goblim/activity/UploadActivity.java

@@ -283,7 +283,7 @@ public class UploadActivity extends AppCompatActivity {
                 runOnUiThread(new Runnable() {
                     @Override
                     public void run() {
-                        if(progressDialog != null) {
+                        if(progressDialog != null && progressDialog.isShowing()) {
                             progressDialog.dismiss();
                             progressDialog = null;
                         }
@@ -522,7 +522,7 @@ public class UploadActivity extends AppCompatActivity {
         //what server we use
         Spinner urlSpinner = (Spinner)findViewById(R.id.servers_spinner);
         int pos = urlSpinner.getSelectedItemPosition();
-        if(urls.size() < pos) {
+        if(urls.size() < pos || pos == Spinner.INVALID_POSITION) {
             runOnUiThread(new Runnable() {
                 @Override
                 public void run() {