Fallback to SMS app for invitations

Fixes #6369
Closes #6400
// FREEBIE

src/org/thoughtcrime/securesms/ConversationActivity.java

@@ -644,9 +644,21 @@ public class ConversationActivity extends PassphraseRequiredActionBarActivity
 
   private void handleInviteLink() {
     try {
+      String inviteText;
+
       boolean a = SecureRandom.getInstance("SHA1PRNG").nextBoolean();
-      if (a) composeText.appendInvite(getString(R.string.ConversationActivity_lets_switch_to_signal, "https://sgnl.link/1LoIMUl"));
-      else   composeText.appendInvite(getString(R.string.ConversationActivity_lets_use_this_to_chat, "https://sgnl.link/1MF56H1"));
+      if (a) inviteText = getString(R.string.ConversationActivity_lets_switch_to_signal, "https://sgnl.link/1LoIMUl");
+      else   inviteText = getString(R.string.ConversationActivity_lets_use_this_to_chat, "https://sgnl.link/1MF56H1");
+
+      if (isDefaultSms) {
+        composeText.appendInvite(inviteText);
+      } else {
+        Intent intent = new Intent(Intent.ACTION_SENDTO);
+        intent.setData(Uri.parse("smsto:" + recipients.getPrimaryRecipient().getNumber()));
+        intent.putExtra("sms_body", inviteText);
+        intent.putExtra(Intent.EXTRA_TEXT, inviteText);
+        startActivity(intent);
+      }
     } catch (NoSuchAlgorithmException e) {
       throw new AssertionError(e);
     }