patch 8.0.1632: in a terminal dump NUL and space are different

Problem:    In a terminal dump NUL and space considered are different,
            although they are displayed the same.
Solution:   When encountering NUL handle it like space.

src/terminal.c

@@ -3396,6 +3396,15 @@ f_term_dumpwrite(typval_T *argvars, typval_T *rettv UNUSED)

	    for (i = 0; i < VTERM_MAX_CHARS_PER_CELL; ++i)
	    {
		int c = cell.chars[i];
		int pc = prev_cell.chars[i];

		/* For the first character NUL is the same as space. */
		if (i == 0)
		{
		    c = (c == NUL) ? ' ' : c;
		    pc = (pc == NUL) ? ' ' : pc;
		}
		if (cell.chars[i] != prev_cell.chars[i])
		    same_chars = FALSE;
		if (cell.chars[i] == NUL || prev_cell.chars[i] == NUL)

src/version.c

@@ -766,6 +766,8 @@ static char *(features[]) =

static int included_patches[] =
{   /* Add new patch number below this line */
/**/
    1632,
/**/
    1631,
/**/