tmread: try different fix for error

tmread.c: In function ‘__libc_termios_insert_editline’:
tmread.c:461:50: error: writing 1 byte into a region of size 0 [-Werror=stringop-overflow=]
  461 |                   __libc_tty_editline.flag[pcol] = _TTY_EDITLINE_SINGLE;
      |                   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~
In file included from ../../../../include/libc/file.h:12,
                 from tmread.c:20:
../../../../include/libc/ttyprvt.h:54:8: note: at offset [-2147483648, -1] into destination object ‘flag’ of size 1024
   54 |   char flag[_TTY_EDITLINE_SIZE];

src/libc/posix/termios/tmread.c

@@ -389,7 +389,7 @@ static void
 __libc_termios_insert_editline (unsigned char ch)
 {
   int mbsize;
-  int col;
+  unsigned int col;
 
   col = __libc_tty_editline.col;
   if (col >= _TTY_EDITLINE_SIZE)
@@ -424,7 +424,7 @@ __libc_termios_insert_editline (unsigned char ch)
     }
   else
     {
-      int pcol;
+      unsigned int pcol;
 
       /* look for non fixed flag */
       pcol = col;
@@ -450,7 +450,7 @@ __libc_termios_insert_editline (unsigned char ch)
 	}
       else
 	{
-	  if ((col - pcol + 1) > MB_CUR_MAX)
+	  if ((col - pcol + 1) > (unsigned)MB_CUR_MAX)
 	    {
 	      /* it's terrible... */
 	      while (pcol <= col)