getdigits: introduce strict, def parameters

Problem:
During a refactor long ago, we changed the `getdigits_*` familiy of
functions to abort on overflow.  But this is often wrong, because many
of these codepaths are handling user input.

Solution:
Decide at each call-site whether to use "strict" mode.

fix #5555

src/nvim/hardcopy.c

@@ -325,7 +325,7 @@ static char_u *parse_list_options(char_u *option_str, option_table_T *table,
         break;
       }
 
-      table[idx].number = getdigits_int(&p);
+      table[idx].number = getdigits_int(&p, false, 0);
     }
 
     table[idx].string = p;