codec/substtml: fix misleading diagnostic
codec/substtml: fix misleading diagnostic

Given that the path handles both "region" and "style" attributes,
unconditionally having warnings that includes usage of "Style" is
rather misleading.

These changes fixes the issue by chaning the warning-diagnostic to
include more relevant information.

Signed-off-by: Hugo Beauzée-Luyssen <3faf7ed52fa83d583fc670a96bcf92da270d0767@beauzee.fr>

xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc