Results are forced to recalculate for cells with General format in
case they need to inherit a format that then can be set. However,
a General format will never lead to some other format being set
for any string results and almost all string result cells will
have General format because the string is already what is being
displayed. So for formula cells with a string result available do
not allow to use ScFormulaCell::SetNeedNumberFormat() forcing the
need to recalculate.

This popped up during intercepting for tdf#118735 when the formula
cell containing a WEBSERVICE() call is set dirty, through
CompileXMLHandler::operator()(...)

    if (pCell->NeedsNumberFormat())
        pCell->SetDirtyVar();

Which again, as WEBSERVICE() has to be recalculated to populate
the link manager, made it necessary to add that to
ScRecalcMode::ONLOAD_LENIENT (which it should already had been
before (when that was ONLOAD), but no harm in this case).

Change-Id: I0dc2cdfe35c56d9843f0edd24a6d14e3de79f7ef
Reviewed-on: https://gerrit.libreoffice.org/57700Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Jenkins