The API functions `command` and `command_options` (when `split_newline` = 0,
which is the default value) don't split on newline and then the first line is
executed and the subsequent lines (after "\n") are ignored.
There are no changes when the input has multiple lines filled by the user: the
split is done and multiple commands are executed (for example if the user is
pasting multiple commands to execute).
Now the function utf8_char_size_screen can return -1 when the char is not
printable.
It has a specific behavior for some chars:
- U+0009: value of option weechat.look.tab_width
- U+0001 to U+001F (except U+0009): 1
- U+00AD (soft hyphen): -1
- U+200B (zero width space): -1
Sébastien Helleu