Evas textblock: fix case of own_closer in style_set

Evas textblock: fix case of own_closer in style_set

Looks like it was assumed that an fnode->orig_format always ends with a
'/' character if the fnode is an own_closer.
The problem is that a paragraph separator ("ps" and "br" - the latter in
legacy newline mode) is also an own_closer, but might not have '/' at the
end, so decrementing the length is wrong.

This fixes T2654. The example markup had "br" read as "b", which led to
a mismatch with the "font_weight=Bold" tag. Coincidentally, "ps" was not
affected as there was no matching "p" in the style.

@fix