justify: reduce the character count when trimming trailing spaces

This fixes https://savannah.gnu.org/bugs/?50379.

src/text.c

@@ -2449,6 +2449,7 @@ void do_justify(bool full_justify)
 		while (break_pos > 0 &&
 			is_blank_mbchar(&openfile->current->data[break_pos - 1])) {
 		    break_pos--;
+		    openfile->totsize--;
 		}
 	    }
 	    null_at(&openfile->current->data, break_pos);