Try to reduce JNI calls into compressor.

Comparatively speaking, JNI calls are very expensive, so we want to
reduce them as much as possible.

native/src/main/java/com/velocitypowered/natives/compression/NativeVelocityCompressor.java

@@ -56,7 +56,7 @@ public class NativeVelocityCompressor implements VelocityCompressor {
       int produced = deflate.process(deflateCtx, source.memoryAddress() + source.readerIndex(),
           source.readableBytes(),
           destination.memoryAddress() + destination.writerIndex(), destination.writableBytes(),
-          !source.isReadable());
+          true);
       source.readerIndex(source.readerIndex() + deflate.consumed);
       destination.writerIndex(destination.writerIndex() + produced);
     }

native/src/test/java/com/velocitypowered/natives/compression/VelocityCompressorTest.java

@@ -36,21 +36,21 @@ class VelocityCompressorTest {
       compressor.dispose();
       fail("Loaded regular compressor");
     }
-    check(compressor, () -> Unpooled.directBuffer(TEST_DATA.length));
+    check(compressor, () -> Unpooled.directBuffer(TEST_DATA.length + 32));
   }
 
   @Test
   void javaIntegrityCheckDirect() throws DataFormatException {
     VelocityCompressor compressor = JavaVelocityCompressor.FACTORY
         .create(Deflater.DEFAULT_COMPRESSION);
-    check(compressor, () -> Unpooled.directBuffer(TEST_DATA.length));
+    check(compressor, () -> Unpooled.directBuffer(TEST_DATA.length + 32));
   }
 
   @Test
   void javaIntegrityCheckHeap() throws DataFormatException {
     VelocityCompressor compressor = JavaVelocityCompressor.FACTORY
         .create(Deflater.DEFAULT_COMPRESSION);
-    check(compressor, () -> Unpooled.buffer(TEST_DATA.length));
+    check(compressor, () -> Unpooled.buffer(TEST_DATA.length + 32));
   }
 
   private void check(VelocityCompressor compressor, Supplier<ByteBuf> bufSupplier)