tdf#153094: it seems that DOC requires WW8_RESERVED_SLOTS = 15

Regression from commit a2a08463e0299d514e6e555ae61c68bb0e4348d0,
where I mistakenly assumed that the value is just to accommodate
enough entries. I don't know where it's documented, but this
fixes the bug.

Change-Id: Ifecf5d294222e3a40cb23f7c147694dbdf35e405
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/145869
Tested-by: Mike Kaganski <mike.kaganski@collabora.com>
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>
(cherry picked from commit dc2ad435cd148a492aba3f2b18bbba0c769f463e)
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/145806
Tested-by: Jenkins
Reviewed-by: Xisco Fauli <xiscofauli@libreoffice.org>
diff --git a/sw/source/filter/ww8/wrtw8sty.cxx b/sw/source/filter/ww8/wrtw8sty.cxx
index f251f41..2d9a346 100644
--- a/sw/source/filter/ww8/wrtw8sty.cxx
+++ b/sw/source/filter/ww8/wrtw8sty.cxx
@@ -122,7 +122,7 @@ public:
//  Styles

// Immediately after reserved slots, character styles begin
#define WW8_RESERVED_SLOTS 10
#define WW8_RESERVED_SLOTS 15 // tdf#153094: the value is important

// GetId( SwCharFormat ) for use in text -> zero is not allowed,
// use "Default Char Style" instead