Fix: IME input displays text after cursor before cursor

When inserting text using IME on a button, the character after the cursor is
displayed before the cursor.

This bug seems to have occurred during the refactoring in D765.

Differential Revision: https://developer.blender.org/D11072

source/blender/editors/interface/interface_widgets.c

@@ -2013,7 +2013,8 @@ static void widget_draw_text(const uiFontStyle *fstyle,
         /* insert composite string into cursor pos */
         BLI_snprintf((char *)drawstr,
                      UI_MAX_DRAW_STR,
-                     "%s%s%s",
+                     "%.*s%s%s",
+                     but->pos,
                      but->editstr,
                      ime_data->str_composite,
                      but->editstr + but->pos);