Fix app licensing request returning invalid response (#3398)

Author: DaVinci9196

vending-app/src/main/java/com/android/vending/licensing/LicenseChecker.kt

@@ -155,7 +155,7 @@ suspend fun HttpClient.makeLicenseV2Request(
     url = "https://play-fe.googleapis.com/fdfe/apps/checkLicenseServerFallback?pkgn=$packageName&vc=$versionCode",
     headers = buildRequestHeaders(auth, androidId),
     adapter = GoogleApiResponse.ADAPTER
-).payload?.licenseV2Response?.license?.jwt?.let {
-    // Field present ←→ user has license
+).payload?.licenseV2Response?.license?.jwt?.takeIf { it.isNotEmpty() }?.let {
+    // Field present and non-empty ←→ user has license
     V2Response(LICENSED, it)
 }

vending-app/src/main/java/com/android/vending/licensing/LicensingService.kt

@@ -75,6 +75,7 @@ class LicensingService : Service() {
              */
             if (response?.result == LICENSED && response is V2Response) {
                 val bundle = Bundle()
+                Log.e(TAG, "checkLicenseV2 jwt: ${response.jwt}")
                 bundle.putString(KEY_V2_RESULT_JWT, response.jwt)
 
                 try {
@@ -143,6 +144,7 @@ class LicensingService : Service() {
 
             // Attempt to acquire license if app is free ("auto-purchase")
             if (isLicensingPurchaseFreeAppsEnabled(this@LicensingService)) {
+                Log.d(TAG, "Attempting to acquire license for free app $packageName")
                 val firstAccount = accounts[0]
                 if (httpClient.acquireFreeAppLicense(
                         this@LicensingService,