Fix Pcbnew search "not found" prompt not displayed

Before this, "Searching..." prompt will not go away if nothing was found
in a search session. A bug I noticed while working on !611. After this
fix, "foo not found" will be displayed when Pcbnew cannot find the
given text.

pcbnew/dialogs/dialog_find.cpp

@@ -335,6 +335,8 @@ void DIALOG_FIND::search( bool aDirection )
         m_frame->SetStatusText( wxEmptyString );
         msg.Printf( _( "\"%s\" not found" ), searchString );
         m_frame->ShowInfoBarMsg( msg );
+
+        m_status->SetLabel( msg );
     }
     else if( endIsReached )
     {