Fix GH-9033: Loading blacklist file can fail due to negative length

If the blacklist file contains a line with a single double-quote, we
called `zend_strndup(pbuf, -1)` what causes an unnecessary bail out;
instead we just ignore that line.

If the blacklist file contains an empty line, we may have caused an OOB
read; instead we just ignore that line.

Closes GH-9036.

Author: cmb69

NEWS

@@ -5,6 +5,10 @@ PHP                                                                        NEWS
 - DBA:
   . Fixed LMDB driver memory leak on DB creation failure (Girgias)
 
+- OPcache:
+  . Fixed bug GH-9033 (Loading blacklist file can fail due to negative length).
+    (cmb)
+
 - Standard:
   . Fixed bug GH-9017 (php_stream_sock_open_from_socket could return NULL).
     (Heiko Weber)

ext/opcache/zend_accelerator_blacklist.c

@@ -276,12 +276,12 @@ static void zend_accel_blacklist_loadone(zend_blacklist *blacklist, char *filena
 		}
 
 		/* strip \" */
-		if (pbuf[0] == '\"' && pbuf[path_length - 1]== '\"') {
+		if (path_length > 0 && pbuf[0] == '\"' && pbuf[path_length - 1]== '\"') {
 			*pbuf++ = 0;
 			path_length -= 2;
 		}
 
-		if (path_length == 0) {
+		if (path_length <= 0) {
 			continue;
 		}