Fix header sync and recovery handling

app/build.gradle.kts

@@ -22,8 +22,8 @@ android {
         applicationId = "org.vextaproject.wallet"
         minSdk = 26
         targetSdk = 36
-        versionCode = 33
+        versionCode = 35
-        versionName = "0.6.3"
+        versionName = "0.6.5"
     }
 
     signingConfigs {

app/src/main/java/org/vextaproject/wallet/HeaderSync.kt

@@ -192,8 +192,13 @@ object HeaderSync {
         val buffer = ByteBuffer.wrap(payload).order(ByteOrder.LITTLE_ENDIAN)
         val count = readCompactSize(buffer)
 
-        if (count > 2000) {
+        val maximumPossibleHeaders =
-            throw IllegalStateException("too many headers: $count")
+            buffer.remaining() / 81
+
+        if (count < 0 || count > maximumPossibleHeaders) {
+            throw IllegalStateException(
+                "invalid headers count: $count"
+            )
         }
 
         repeat(count) {

app/src/main/java/org/vextaproject/wallet/MainActivity.kt

@@ -148,6 +148,7 @@ class MainActivity : Activity() {
 
                 runOnUiThread {
                     if (intent.getBooleanExtra("sync_only", false)) {
+                        if (chain.last().height > 0) {
                             setResult(
                                 RESULT_OK,
                                 android.content.Intent().putExtra(
@@ -155,6 +156,15 @@ class MainActivity : Activity() {
                                     chain.last().height
                                 )
                             )
+                        } else {
+                            setResult(
+                                RESULT_CANCELED,
+                                android.content.Intent().putExtra(
+                                    "sync_error",
+                                    results.joinToString("\n\n")
+                                )
+                            )
+                        }
                         finish()
                     } else {
                         status.text =
@@ -317,8 +327,13 @@ class MainActivity : Activity() {
         val buffer = ByteBuffer.wrap(payload).order(ByteOrder.LITTLE_ENDIAN)
         val count = readCompactSize(buffer)
 
-        if (count > 2000) {
+        val maximumPossibleHeaders =
-            throw IllegalStateException("too many headers: $count")
+            buffer.remaining() / 81
+
+        if (count < 0 || count > maximumPossibleHeaders) {
+            throw IllegalStateException(
+                "invalid headers count: $count"
+            )
         }
 
         repeat(count) {

app/src/main/java/org/vextaproject/wallet/WalletActivity.kt

@@ -871,8 +871,18 @@ class WalletActivity : FragmentActivity() {
                 runBlockchainScan()
             } else {
                 blockchainScanRunning = false
+
+                val syncError = data?.getStringExtra(
+                    "sync_error"
+                )?.trim()
+
                 blockchainScanStatus?.text =
+                    if (syncError.isNullOrBlank()) {
                         "Block-header synchronization failed."
+                    } else {
+                        "Block-header synchronization failed:\n" +
+                            syncError
+                    }
             }
 
             return