[vala] Check left parameter of is

[Florian Brosch <flobrosch src gnome org>]

commit 516e73a9b12c7d096d42976518949c1b641540e4
Author: Florian Brosch <flo brosch gmail com>
Date:   Tue Jan 17 22:08:19 2012 +0100

    Check left parameter of is

 vala/valatypecheck.vala |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)
---
diff --git a/vala/valatypecheck.vala b/vala/valatypecheck.vala
index 749401d..de3d30a 100644
--- a/vala/valatypecheck.vala
+++ b/vala/valatypecheck.vala
@@ -104,6 +104,12 @@ public class Vala.TypeCheck : Expression {
 		
 		type_reference.check (context);
 
+		if (expression.value_type == null) {
+			Report.error (expression.source_reference, "invalid left operand");
+			error = true;
+			return false;
+		}
+
 		if (type_reference.data_type == null) {
 			/* if type resolving didn't succeed, skip this check */
 			error = true;