Adds a fix for ThrowIfRector causing issues with assigned vars

[peterfox]

Changes

• alters the IfThrowRector rule
• adds more test scenarios

Why

Sometimes the rule could generate broken code where a variable might not exist as it's created in the If statement's condition. In this instance the rule shouldn't make any changes.

if ($foo && $bar = call()) {
    throw new Exception($foo, $bar);
}