fix: resolve regression made in #1164

[qweeah]

What this PR does / why we need it:
#1164 has a regression which only print skip hints for empty layers. This PR fixed it. Tested with below command. Will add E2E tests to cover all possibility for the skip hint

✗ ./bin/linux/amd64/oras pull ghcr.io/oras-project/oras:v1.1.0 -o pulled --platform linux/amd64
✓ Skipped     application/vnd.oci.image.layer.v1.tar+gzip                                                                                                                                                                                                                                            3.21/3.21 MB 100.00%     0s
  └─ sha256:8921db27df2831fa6eaa85321205a2470c669b855f3ec95d5a3c2b46de0442c9 
✓ Skipped     application/vnd.oci.image.layer.v1.tar+gzip                                                                                                                                                                                                                                            2.74/2.74 MB 100.00%     0s
  └─ sha256:c03f8561538a489bffa3df71a54f0bb1d61b73b1146e9afaefff90264972d15d 
✓ Skipped     application/vnd.oci.image.layer.v1.tar+gzip                                                                                                                                                                                                                                            3.57/3.57 MB 100.00%     0s
  └─ sha256:fb7cddd3bf538e066da2433159de5b759336497e6e6d14b0d30097f6fee60436 
✓ Skipped     application/vnd.oci.image.layer.v1.tar+gzip                                                                                                                                                                                                                                                97/97  B 100.00%     0s
  └─ sha256:5165500f6395b142b9c4ea6dff0d4ead798b45f36d60559f1023970edb3d9bc2 
✓ Skipped     application/vnd.oci.image.layer.v1.tar+gzip                                                                                                                                                                                                                                                32/32  B 100.00%     0s
  └─ sha256:4f4fb700ef54461cfa02571ae0db9a0dc1e0cdb5577484a6d75e68dc38e8acc1 
✓ Skipped     application/vnd.oci.image.config.v1+json                                                                                                                                                                                                                                               1.57/1.57 kB 100.00%     0s
  └─ sha256:7f6a5a12676c0e61ab4847cddee29d4dac535cf10fd1c2c76d501911d892cd40 
✓ Pulled      application/vnd.oci.image.manifest.v1+json                                                                                                                                                                                                                                             1.21/1.21 kB 100.00%     0s 
  └─ sha256:b54d7405f956d7219523a4cd54cf1c6fb4820099e234c0e14566a5113874e7c5 
Skipped pulling layers without file name in "org.opencontainers.image.title"
Use 'oras copy ghcr.io/oras-project/oras:v1.1.0 --to-oci-layout <layout-dir>' to pull all layers.

[codecov-commenter]

Codecov Report

Merging #1170 (d1cd96c) into main (d9b2c5c) will increase coverage by 0.19%.
The diff coverage is 50.00%.

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@@            Coverage Diff             @@
##             main    #1170      +/-   ##
==========================================
+ Coverage   79.84%   80.03%   +0.19%     
==========================================
  Files          65       65              
  Lines        3547     3551       +4     
==========================================
+ Hits         2832     2842      +10     
+ Misses        498      494       -4     
+ Partials      217      215       -2     

Files	Coverage Δ
cmd/oras/root/pull.go	74.43% <50.00%> (+2.29%)	⬆️

... and 1 file with indirect coverage changes