into an existing document since....

commit deaa16bd
Author: Serge Krot <Serge.Krot@cib.de>
Date:   Mon Jan 29 12:17:06 2018 +0100

    tdf#72942 Do not overwrite styles from the inserted doc

    During inserting of the text from the external document
    we should not change original default styles in
    currently opened document.

because missing styles aren't created, so there's exceptons
thrown on their use.

I see that the m_bIsNewDoc flag is already checked for since...

commit 5ebe826c
Author: Miklos Vajna <vmiklos@collabora.co.uk>
Date:   Fri Oct 4 11:02:59 2013 +0200

    fdo#69384 fix impress -> writer copy&paste

    Regression from 2ade0712 (fdo#62044 RTF
    import: don't overwrite existing styles when pasting, 2013-06-04),
    during paste, if existing style was found, then the intention was to
    skip that style, but instead we tried to create one.

in the body of the following loop, which should mean that existing
styles are left alone and only missing styles created if we remove
this hunk of the tdf#72942 commit

Change-Id: Ia4aedb5e309c991490656061aa20d11ff24f4f9e
Reviewed-on: https://gerrit.libreoffice.org/59519
Tested-by: Jenkins
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>