Fix use-of-uninitialized-value ast->lineno

Exposed after GH-22833. ast->kind in this context may refer to a ZEND_AST_ZVAL,
for which accessing lineno is incorrect. lineno is stored in zval.u2 instead.

Fixes OSS-Fuzz-539121135

Author: iluuu1994

Zend/tests/oss-fuzz-539121135.phpt

@@ -0,0 +1,12 @@
+--TEST--
+OSS-Fuzz-539121135: Use-of-uninitialized-value ast->lineno
+--FILE--
+<?php
+
+namespace {}
+
+''
+
+?>
+--EXPECTF--
+Fatal error: No code may exist outside of namespace {} in %s on line %d

Zend/zend_compile.c

@@ -12215,7 +12215,7 @@ static void zend_compile_stmt(zend_ast *ast) /* {{{ */
 		return;
 	}
 
-	CG(zend_lineno) = ast->lineno;
+	CG(zend_lineno) = zend_ast_get_lineno(ast);
 
 	if ((CG(compiler_options) & ZEND_COMPILE_EXTENDED_STMT) && !zend_is_unticked_stmt(ast)) {
 		zend_do_extended_stmt(NULL);