fix crash in getReturnTypeFromFunctionBody if function declaration is incomplete and does not have body

src/compiler/checker.ts

@@ -6525,6 +6525,9 @@ module ts {
 
         function getReturnTypeFromBody(func: FunctionLikeDeclaration, contextualMapper?: TypeMapper): Type {
             var contextualSignature = getContextualSignatureForFunctionLikeDeclaration(func);
+            if (!func.body) {
+                return unknownType;
+            }
             if (func.body.kind !== SyntaxKind.Block) {
                 var type = checkExpressionCached(<Expression>func.body, contextualMapper);
             }

tests/cases/fourslash/errorInIncompleteMethodInObjectLiteral.ts

@@ -0,0 +1,5 @@
+/// <reference path='fourslash.ts'/>
+
+//// var x: { f(): string } = { f( }
+
+verify.numberOfErrorsInCurrentFile(1);