Editor: Update current argument in function hint

Notify the codeassistant that something has changed when the function
hint widget is visible and a key was released.

Fixes: QTCREATORBUG-24449
Change-Id: Iab6c6a13fd91485b077fbd1a812a16e32d558596
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/texteditor/codeassist/functionhintproposalwidget.cpp

@@ -292,6 +292,8 @@ bool FunctionHintProposalWidget::eventFilter(QObject *obj, QEvent *e)
                 if (d->m_model && d->m_model->size() > 1)
                     return false;
             }
+            if (QTC_GUARD(d->m_assistant))
+                d->m_assistant->notifyChange();
         }
         break;
     case QEvent::WindowDeactivate: