Updater: don't immediately retry if check fails

If something goes wrong, maybe it's best not to DoS the update server.
Instead back off gradually and then go into the usual sleep loop.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

ui/src/main/java/com/wireguard/android/updater/Updater.kt

@@ -410,18 +410,24 @@ object Updater {
                 return@launch
 
             var waitTime = 15
+            var exceptionCount = 0
             while (true) {
                 try {
-                    val update = checkForUpdates() ?: continue
+                    val update = checkForUpdates() ?: throw Exception("No updates found")
                     if (update.version > CURRENT_VERSION) {
                         Log.i(TAG, "Update available: ${update.version}")
                         UserKnobs.setUpdaterNewerVersionSeen(update.version.toString())
                         return@launch
                     }
                 } catch (_: Throwable) {
+                    if (++exceptionCount <= 6) {
+                        delay((exceptionCount * 8).seconds)
+                        continue
+                    }
                 }
                 delay(waitTime.minutes)
                 waitTime = 45
+                exceptionCount = 0
             }
         }