Fix php_pgsql_fd_cast() wrt. php_stream_can_cast()

`php_stream_can_cast()` forwards to `_php_stream_cast()` with `ret` set
to `NULL`.  `php_pgsql_fd_cast()` needs to cater to that, because
otherwise the stream would report that it is not castable.

This *might* fix https://bugs.php.net/73903.

Closes GH-6888.

NEWS

@@ -8,6 +8,9 @@ PHP                                                                        NEWS
   . Fixed bug #80960 (opendir() warning wrong info when failed on Windows).
     (cmb)
 
+- pgsql:
+  . Fixed php_pgsql_fd_cast() wrt. php_stream_can_cast(). (cmb)
+
 - SPL:
   . Fixed bug #80933 (SplFileObject::DROP_NEW_LINE is broken for NUL and CR).
     (cmb, Nikita)

ext/pgsql/pgsql.c

@@ -5418,16 +5418,17 @@ static int php_pgsql_fd_cast(php_stream *stream, int cast_as, void **ret) /* {{{
 	switch (cast_as)	{
 		case PHP_STREAM_AS_FD_FOR_SELECT:
 		case PHP_STREAM_AS_FD:
-		case PHP_STREAM_AS_SOCKETD:
-			if (ret) {
+		case PHP_STREAM_AS_SOCKETD: {
 				int fd_number = PQsocket(pgsql);
 				if (fd_number == -1) {
 					return FAILURE;
 				}
 
-				*(php_socket_t *)ret = fd_number;
-				return SUCCESS;
+				if (ret) {
+					*(php_socket_t *)ret = fd_number;
+				}
 			}
+			return SUCCESS;
 		default:
 			return FAILURE;
 	}