Fix save task when pressing back

Closes #23

astrid/src/main/AndroidManifest.xml

@@ -7,7 +7,7 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
           package="org.tasks"
           android:versionName="4.6.8"
-          android:versionCode="317">
+          android:versionCode="319">
           
   <!-- widgets, alarms, and services will break if Astrid is installed on SD card -->
   <!--    android:installLocation="internalOnly"> -->

astrid/src/main/java/com/todoroo/astrid/activity/TaskEditFragment.java

@@ -861,7 +861,11 @@ ViewPager.OnPageChangeListener, EditNoteActivity.UpdatesChangedListener {
 
     public boolean onKeyDown(int keyCode) {
         if (keyCode == KeyEvent.KEYCODE_BACK) {
-            discardButtonClick();
+            if(title.getText().length() == 0) {
+                discardButtonClick();
+            } else {
+                saveButtonClick();
+            }
             return true;
         }
         return false;