Description:
------------
Problem
=======
mail throws this fatal error if an additional_parameters (even if it is an empty string) is passed to the function:
PHP Fatal error:  mail(): Escaped command exceeds the allowed length of 8192 bytes

Cause
=====
In the mail function, the extra_cmd is escaped with php_escape_shell_cmd:
https://github.com/php/php-src/blob/master/ext/standard/mail.c#L374

This is incorrect if the string is not passed to an executable. This is the case on Windows when SMTP is used (php.ini: mail.SMTP).

Solution
========
The additional_parameters argument should be ignored (and therefore not be escaped) if it is not used (not passed to a shell command). 

Also there seems to be another bug where php_escape_shell_cmd fails if an empty string is passed.

Test script:
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mail("test@test.com", "subject", "message", "From: lala@test.com", "");

Actual result:
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PHP Fatal error:  mail(): Escaped command exceeds the allowed length of 8192 bytes