[DeadCode] Skip RemoveDeadIfBlockRector on empty if with elseif and trailing else

[TomasVotruba]

Fixes rectorphp/rector#9884

RemoveDeadIfBlockRector changed behavior on an empty if body followed by elseif and a trailing else:

if (in_array($a, $b)) {
} elseif (in_array($a, $c)) {
    echo "elseif";
} else {
    echo "else";
}

was merged into:

if (!in_array($a, $b) && in_array($a, $c)) {
    echo "elseif";
} else {
    echo "else";
}

When the original if condition was true, the empty body ran nothing. After the merge the negated condition is false, so the else branch runs instead - a semantic change.

The merge is only safe when there is no trailing else. This bails out and keeps the code unchanged when an else is present. The existing empty_if_with_elseif_and_else.php.inc fixture (which encoded the wrong output) becomes a skip_ fixture.

https://claude.ai/code/session_01MszFhfN8nK7KR3mBjda8P2