msg: use dynamic buffer for message formatting

Until now, a rather large stack buffer was used for this, and also a
static buffer in mp_log_root. The latter was added to buffer partial
lines, and the stack buffer was used only for MSGL_STATUS and MSGL_STATS
(I guess because these are the most likely/severe to clash with partial
line buffering).

Make the buffer in mp_log_root dynamically sized, so we don't get cut
off log lines if the text is excessively large. (The OpenGL extension
list dumped by vo_opengl is such an example.)

Since we still have to support partial line buffering (FFmpeg's log
callbacks leave no other choice), keep the stack buffer. But make it
smaller; there's no way all ~6KB are going to be needed in any
situation.

0 files changed, 0 insertions, 0 deletions