fix for KT-796/797 candidate/resultingDescriptor misuse

compiler/backend/src/org/jetbrains/jet/codegen/ExpressionCodegen.java

@@ -2199,7 +2199,7 @@ public class ExpressionCodegen extends JetVisitor<StackValue, StackValue> {
                 if(getterDescriptor.getReceiverParameter().exists()) {
                     index++;
                 }
-                for (TypeParameterDescriptor typeParameterDescriptor : getterDescriptor.getTypeParameters()) {
+                for (TypeParameterDescriptor typeParameterDescriptor : resolvedGetCall.getCandidateDescriptor().getTypeParameters()) {
                     if(typeParameterDescriptor.isReified()) {
                         generateTypeInfo(resolvedGetCall.getTypeArguments().get(typeParameterDescriptor), null);
                         index++;

compiler/testData/codegen/regressions/kt796_797.jet

@@ -0,0 +1,8 @@
+fun <T> Array<T>?.get(i : Int?) = this.sure().get(i.sure())
+fun <T> array(vararg t : T) : Array<T> = t
+
+fun box() : String {
+    val a : Array<String>? = array<String>("Str", "Str2")
+    val i : Int? = 1
+    return if(a[i] == "Str2") "OK" else "fail"
+}

compiler/tests/org/jetbrains/jet/codegen/VarArgTest.java

@@ -74,4 +74,8 @@ public class VarArgTest extends CodegenTestCase {
         createEnvironmentWithFullJdk();
         blackBoxFile("regressions/kt581.jet");
     }
+
+    public void testKt797() {
+        blackBoxFile("regressions/kt796_797.jet");
+    }
 }