MFH Fix bug #48493 - spl_autoload_register can leave the HT in an inconsistent way.

Need to point the second elements previous item to head so we can traverse upwards.

ext/spl/php_spl.c

@@ -415,6 +415,7 @@ PHP_FUNCTION(spl_autoload_call)
 	(ht)->pListTail->pListNext = (ht)->pListHead;			\
 	(ht)->pListHead = (ht)->pListTail;						\
 	(ht)->pListTail = (ht)->pListHead->pListLast;			\
+	(ht)->pListHead->pListNext->pListLast = (ht)->pListHead;\
 	(ht)->pListTail->pListNext = NULL;						\
 	(ht)->pListHead->pListLast = NULL;
 

ext/spl/tests/bug48493.phpt

@@ -0,0 +1,26 @@
+--TEST--
+SPL: Bug #48493 spl_autoload_unregister() can't handle prepended functions
+--FILE--
+<?php
+function autoload1() {}
+
+function autoload2() {}
+
+spl_autoload_register('autoload2');
+spl_autoload_register('autoload1', true, true);
+var_dump(spl_autoload_functions());
+
+spl_autoload_unregister('autoload2');
+var_dump(spl_autoload_functions());
+?>
+--EXPECT--
+array(2) {
+  [0]=>
+  string(9) "autoload1"
+  [1]=>
+  string(9) "autoload2"
+}
+array(1) {
+  [0]=>
+  string(9) "autoload1"
+}