filer: keep compressed chunks on the whole-chunk path

Like ciphered chunks, a range request on a compressed chunk makes the
volume server read and decompress the whole needle, so range-per-buffer
would repeat the full backend read for each 256KiB window. Route them
through the shared whole-chunk path via ChunkView.CanRangeFetch.

weed/filer/reader_cache.go

@@ -100,11 +100,11 @@ func (rc *ReaderCache) MaybeCache(chunkViews *Interval[*ChunkView], count int) {
 			// abort when slots are filled
 			return
 		}
-		if chunkView.CipherKey == nil && !chunkView.IsFullChunk() {
+		if chunkView.CanRangeFetch() && !chunkView.IsFullChunk() {
 			// the view is clipped to part of the chunk and will be
 			// range-fetched, so prefetching it whole would download bytes
-			// nobody needs; a ciphered partial view needs the whole blob
-			// anyway and is worth prefetching
+			// nobody needs; a ciphered or compressed partial view needs
+			// the whole blob anyway and is worth prefetching
 			continue
 		}