[vala] Fix crash with virtual async methods

[Jürg Billeter <juergbi src gnome org>]

commit 7f913d96ae72c080bfa5a2d6d90e744db37b53e4
Author: Jürg Billeter <j bitron ch>
Date:   Sun Sep 13 18:09:58 2009 +0200

    Fix crash with virtual async methods

 codegen/valaccodemethodmodule.vala |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)
---
diff --git a/codegen/valaccodemethodmodule.vala b/codegen/valaccodemethodmodule.vala
index b38f4c1..281c44a 100644
--- a/codegen/valaccodemethodmodule.vala
+++ b/codegen/valaccodemethodmodule.vala
@@ -845,7 +845,9 @@ internal class Vala.CCodeMethodModule : CCodeStructModule {
 
 	public void generate_vfunc (Method m, DataType return_type, Map<int,CCodeFormalParameter> cparam_map, Map<int,CCodeExpression> carg_map, string suffix = "", int direction = 3) {
 		var vfunc = new CCodeFunction (m.get_cname () + suffix);
-		vfunc.line = function.line;
+		if (function != null) {
+			vfunc.line = function.line;
+		}
 
 		var vblock = new CCodeBlock ();