Enable -Wconversion: ui.c.

Refactoring summary:
- ui_write(): len: int --> size_t
    * parse_abstract_ui_codes(): len: int --> size_t
    * string_convert(): lenp: int * --> size_t *
        - string_convert_ext(): lenp      : int * --> size_t *
                                unconvlenp: int * --> size_t *
            * utf8len_tab_zero: char[] --> uint8_t[]
            * iconv_string(): slen      : int --> size_t
                              unconvlenp: int * --> size_t *
                              resultlenp: int * --> size_t *
        - mch_print_text_out(): len: int --> size_t
    * out_pos: int --> size_t

1 files changed, 2 insertions, 2 deletions

diff --git a/src/nvim/ui.c b/src/nvim/ui.c
index af8989f397..c09cca1347 100644
--- a/src/nvim/ui.c
+++ b/src/nvim/ui.c
@@ -95,7 +95,7 @@ void ui_builtin_stop(void)
   UI_CALL(stop);
 }
 
-void ui_write(uint8_t *s, int len)
+void ui_write(uint8_t *s, size_t len)
 {
   if (silent_mode && !p_verbose) {
     // Don't output anything in silent mode ("ex -s") unless 'verbose' set
@@ -346,7 +346,7 @@ end:
   UI_CALL(highlight_set, (ui->rgb ? rgb_attrs : cterm_attrs));
 }
 
-static void parse_abstract_ui_codes(uint8_t *ptr, int len)
+static void parse_abstract_ui_codes(uint8_t *ptr, size_t len)
 {
   if (!ui_active()) {
     return;