Rewind ByteBuffers in ByteBufferUtil.toFile.

This avoids writing partial data if the buffer is not at position 0 when the method is called. This fixes a bug where using DiskCacheStrategy.ALL
or DiskCacheStrategy.RESOURCE with GifDrawables would result in partial
and invalid gif files being written to Glide’s disk cache.

library/src/main/java/com/bumptech/glide/util/ByteBufferUtil.java

@@ -53,6 +53,7 @@ public static ByteBuffer fromFile(File file) throws IOException {
   }
 
   public static void toFile(ByteBuffer buffer, File file) throws IOException {
+    buffer.position(0);
     RandomAccessFile raf = null;
     FileChannel channel = null;
     try {