Set decoder thread priority to default

The priority of a decode thread was THREAD_PRIORITY_BACKGROUND. It may cause a long time waiting before image decoded.

app/src/main/java/com/hippo/ehviewer/spider/SpiderQueen.java

@@ -834,8 +834,9 @@ public final class SpiderQueen implements Runnable {
         tryToEnsureWorkers();
 
         // Start spider decoder
-        Thread decoderThread = new PriorityThread(new SpiderDecoder(), "SpiderDecoder-" + sIdGenerator.incrementAndGet(),
-                Process.THREAD_PRIORITY_BACKGROUND);
+        Thread decoderThread = new PriorityThread(new SpiderDecoder(),
+                "SpiderDecoder-" + sIdGenerator.incrementAndGet(),
+                Process.THREAD_PRIORITY_DEFAULT);
         mDecoderThread = decoderThread;
         decoderThread.start();