Bugfix nick completion / autocorrect

Use clearComposingText() when inserting nick completion to ensure
that autocorrect doesn't try to replace the completed nick on the next
keypress; thanks Thomas Martitz for pointing out the bug

application/src/org/yaaic/activity/ConversationActivity.java

@@ -939,6 +939,7 @@ public class ConversationActivity extends Activity implements ServiceConnection,
         input.getText().replace(start, end, nick, 0, nick.length());
         // put cursor after inserted text
         input.setSelection(start + nick.length());
+        input.clearComposingText();
         input.post(new Runnable() {
             @Override
             public void run() {