When you add a feed url and clear the input after entering some
characters, then the error label is shown. The empty url check in the
code is broken, because it is performed on a version of the url which
is not the original input and instead a version modified in the code.
I store in a variable whether the original input url is empty.
part of #45
When you enter an invalid or duplicate URL an error message is shown.
But GTK's error style is not applied to the entry.
This commit applies GTK's error style to the URL entry when appropriate.
part of #45
Validation errors of an entry should be displayed by an icon with a
tooltip explaining the reason.
For the situation when you add a podcast URL I remove the existing
error label and show the former label text as tooltip of an error icon
in the entry.
FeuRenard