Now the function utf8_next_char with an empty string returns NULL instead of
the next char, which is most of the time after an allocated buffer.
And the function utf8_char_size with an empty string now returns 0 instead of
1.
This indirectly fixes a buffer overflow in function eval_string_range_chars
when the input string is empty (for example when doing `/eval -n ${chars:}`).
At the moment, building WeeChat triggers several thousand -Wstrict-prototypes
diagnostics. This is due to its source code using an empty argument list for
functions and function pointers that take no arguments, instead of explicitly
declaring that they take no arguments by using a void list.
This commit replaces all empty argument lists with a void list.
Note that Ruby's headers also suffer the same problem, which WeeChat can't
do anything to fix. Thus, building WeeChat with the Ruby plugin enabled
will still issue approximately 30 such diagnostics.
Sébastien Helleu