Fix function declaration without body to be checked as context sensitive

Fixes #29032

src/compiler/checker.ts

@@ -11040,8 +11040,7 @@ namespace ts {
 
         function hasContextSensitiveReturnExpression(node: FunctionLikeDeclaration) {
             // TODO(anhans): A block should be context-sensitive if it has a context-sensitive return value.
-            const body = node.body!;
-            return body.kind === SyntaxKind.Block ? false : isContextSensitive(body);
+            return !node.body || node.body.kind === SyntaxKind.Block ? false : isContextSensitive(node.body);
         }
 
         function isContextSensitiveFunctionOrObjectLiteralMethod(func: Node): func is FunctionExpression | ArrowFunction | MethodDeclaration {

tests/cases/fourslash/quickInfoTypeArgumentInferenceWithMethodWithoutBody.ts

@@ -0,0 +1,16 @@
+/// <reference path='fourslash.ts' />
+
+////interface ProxyHandler<T extends object> {
+////    getPrototypeOf?(target: T): object | null;
+////}
+////interface ProxyConstructor {
+////    new <T extends object>(target: T, handler: ProxyHandler<T>): T;
+////}
+////declare var Proxy: ProxyConstructor;
+////let target = {}
+////let proxy = new /**/Proxy(target, {
+////    getPrototypeOf()
+////})
+
+goTo.marker("");
+verify.quickInfoExists();