Description:
------------
htmlspecialchars() does not always detect bad character set argument.

Problem in the following code around line 850 of ext/standard/html.c:

det_charset:

	if (charset_hint) {
	   int found = 0;
		
	    /* now walk the charset map and look for the codeset */
		for (i = 0; charset_map[i].codeset; i++) {
			if (strncasecmp(charset_hint, charset_map[i].codeset, len) == 0) {
		           charset = charset_map[i].charset;
			   found = 1;
			   break;
			}
		}

This uses "len" as the maximum comparison length which is the length 
of the input charset hint. If this happens to match the first few 
characters of a VALID charset then the code fails to detect a bad 
charset. For example  a charset_hint of "125" is allowed as it matches
the first 3 characters of a valid charset; namely "1252".

If code is changed as follows to check the length as are equal first 
then the problem is resolved. 

		for (i = 0; charset_map[i].codeset; i++) {
			if (len == strlen(charset_map[i].codeset) && strncasecmp(charset_hint, charset_map[i].codeset, len) == 0) {
				charset = charset_map[i].charset;
				found = 1;
				break;
			}
		}

Reproduce code:
---------------
<?php
var_dump( htmlspecialchars("<a href='test'>Test</a>", ENT_COMPAT, 1) );
var_dump( htmlspecialchars("<a href='test'>Test</a>", ENT_COMPAT, 12) );
var_dump( htmlspecialchars("<a href='test'>Test</a>", ENT_COMPAT, 125) );
var_dump( htmlspecialchars("<a href='test'>Test</a>", ENT_COMPAT, 1252) );
var_dump( htmlspecialchars("<a href='test'>Test</a>", ENT_COMPAT, 12526) );

?>
===Done===

Expected result:
----------------
PHP Warning:  htmlspecialchars(): charset `1' not supported, assuming iso-8859-1 in  <path to t/c> 
string(35) "&lt;a href='test'&gt;Test&lt;/a&gt;"
PHP Warning:  htmlspecialchars(): charset `12' not supported, assuming iso-8859-1 in <path to t/c> 
string(35) "&lt;a href='test'&gt;Test&lt;/a&gt;"
PHP Warning:  htmlspecialchars(): charset `125' not supported, assuming iso-8859-1 in <path to t/c> 
string(35) "&lt;a href='test'&gt;Test&lt;/a&gt;"
string(35) "&lt;a href='test'&gt;Test&lt;/a&gt;"
PHP Warning:  htmlspecialchars(): charset `12526' not supported, assuming iso-8859-1 in <path to t/c> 
string(35) "&lt;a href='test'&gt;Test&lt;/a&gt;"
===Done===

Actual result:
--------------
string(35) "&lt;a href='test'&gt;Test&lt;/a&gt;"
string(35) "&lt;a href='test'&gt;Test&lt;/a&gt;"
string(35) "&lt;a href='test'&gt;Test&lt;/a&gt;"
string(35) "&lt;a href='test'&gt;Test&lt;/a&gt;"
PHP Warning:  htmlspecialchars(): charset `12526' not supported, assuming iso-8859-1 in  <path to t/c> 
string(35) "&lt;a href='test'&gt;Test&lt;/a&gt;"
===Done===