Update srand.xml Fix incorrect description (php#4871)

* Update srand.xml Fix incorrect description

`srand(0)` uses `0` as seed, random seeding only occurs when seed is `null` or omitted.

* Update srand.xml Sync the description with mt_srand()

Author: mmalferov

reference/random/functions/srand.xml

@@ -13,8 +13,9 @@
    <methodparam choice="opt"><type>int</type><parameter>mode</parameter><initializer><constant>MT_RAND_MT19937</constant></initializer></methodparam>
   </methodsynopsis>
   <para>
-   Seeds the random number generator with <parameter>seed</parameter>
-   or with a random value if <parameter>seed</parameter> is <literal>0</literal>.
+   Seeds the random number generator with
+   <parameter>seed</parameter> or with a random value
+   if no <parameter>seed</parameter> is given.
   </para>
 
   &note.randomseed;