fix(messages): compute msg_col after last newline in ext_messages

Problem:  We want to keep track of the current message column, which is
          done very rudimentary for ext_messages; only checking if the
          message ends in a newline to reset the column, while computing
          the entire cellwidth of the message, which may contain
          (multiple) newlines not necessarily at the end (since 21718c6).
          This introduced a noticeable delay for large messages (e.g. :=vim).
Solution: Calculate the cellwidth of the message after the last newline.
          Use it to keep track of the current message column. This might
          not be a functional change currently, since it only affects
          messages with (multiple) newlines not at the end of a message,
          which I don't think we emit internally, and msg_col is reset for
          a new kind. It does fix the performance problem.

0 files changed, 0 insertions, 0 deletions