Filip Roséen authored Sep 19, 2016 and Hugo Beauzée-Luyssen committed Sep 20, 2016

If MergeStyles was invoked with *pp_dest == NULL, the resulting string
would contain unspecified/undefined data (given that passing NULL as
value for the corresponding format-specifier is undefined-behavior).

Most platforms will either print "" or "(null)" for such cases, and
the latter will cause problems with the decoder.

These changes fixes the issue by explicitly printing an empty string
if "*pp_dest == NULL".

fixes #17414

Signed-off-by: Hugo Beauzée-Luyssen <hugo@beauzee.fr>