Fix #74267: segfault with streams and invalid data

[cmb69]

If the current character is a line break character, it cannot be a tab
or space character, so we would always fail with an invalid sequence
error. Obviously, these conditions are meant to be exclusive.

[nikic]

This change looks right to me, but it's not immediately clear how it leads to a segfault. From a cursory reading, it would just caused an invalid sequence error.

[cmb69]

The segfaults happens in the final call to that function, because the following condition is false then (lb_cnt==1, lb_ptr==0):

php-src/ext/standard/filters.c

Line 1019 in ceae816

if ((in_pp == NULL || in_left_p == NULL) && lb_cnt == lb_ptr) {

but shortly after in_pp and in_left_p (both being NULL) are dereferenced. It seems to me that the additional constraint (&& lb_cnt == lb_ptr) is not correct, but even if I remove it, there would be three warnings regarding invalid sequences, although there are only two invalid sequences in the test.

[nikic]

@cmb69 Shouldn't we fix that condition as well? It's not clear to me that there is no other code path that could run into the same issue.

[cmb69]

Yes, you're right. These constraints don't make sense.

[cmb69]

Thanks! Applied as 12c59f6.