Fix popup error due to uninitialized members

Fix popup error due to uninitialized members

Add code to initialize member variables in Popup's constructor and
to check whether the value from elm_entry_entry_get() is null or not

When cert popups are opened in succession, elm_entry_entry_get() returns
null occationally. So it needs null check.

Until now, Popup's boolean member variables have not initialized. So
Popup::Result() enters code about entry although Popup doesn't use entry.
It needs to initialize member variables with proper values.