replay: Handle external definition parsing error
It exist cases where an external definition defined on a path is malformed resulting in a parsing error from the official subversion client.
In that case, externals defined on that path will not be processed when exporting a revision.
(swh) anlambert@carnavalet:/tmp$ svn export https://svn.code.sf.net/p/modelbuilder/code@642 modelbuilder
A modelbuilder
A modelbuilder/src
A modelbuilder/src/trunk
A modelbuilder/src/trunk/contrib
A modelbuilder/src/trunk/contrib/symbolic
...
A modelbuilder/html/images/icon_linux.gif
A modelbuilder/html/create.bat
A modelbuilder/html/download.fp
svn: E195005: Error parsing svn:externals property on '/tmp/modelbuilder/src/trunk/contrib': 'symbolic -r1288http://svn.freepascal.org/svn/fpcprojects/contrib/symbolic/'
So align loader behavior with official subversion client.
Fixes SWH-LOADER-SVN-7J
Migrated from D7555 (view on Phabricator)