win32: UTF8_OUTPUT: recover quicker from bad byte

When an unexpected value is detected in UTF-8, we should print the
placeholder codepoint, and then recover whenever we detect a value
which is valid for starting a new UTF-8 codepoint (including ASCII7).

However, previously, we only tested recovery at the bytes following
the unexpected one, and so if the first unexpected value was also
valid for a new codepoint, then didn't rcover it.

Now we check for recovery from the first unexpected byte, which,
if recoverable, requires both placeholder printout and recovery,
so the recovery "unwinding" is modified a bit to allow placeholder.

Example of of a sequence which now recovers quicker than before:
(where UTF-8 for U+1F600 "😀" is: 0xF0 0x9F 0x98 0x80)

  printf "\xF0\xF0\x9F\x98\x80A"

Previously: ?A
Now:        ?😀A

0 files changed, 0 insertions, 0 deletions