Handle unmarshall unknown aliases

[nervo]

Right now, trying to unmarshall invalid yaml (with unknown aliases) using custom unmarshallers lead to a panic.

See: https://go.dev/play/p/3DT9zna3Mft

This is due to decode:resolveAlias (resolveAlias) method which could not handle errors, and its AliasNode switch case (

go-yaml/decode.go

Line 293 in ecececd

case *ast.AliasNode:

) which don't check the presence of an alias in anchorNodeMap before returning a node.
If an alias is unknown, decode:resolveAlias returns nil, breaking all subsequents handlings.

This pr introduce errors handling in resolveAlias, and its related methods unmarshalableDocument & unmarshalableText. It also checks that an alias is present in the anchorNodeMap an returns error if not.

[codecov-commenter]

Codecov Report

Merging #317 (ec3ae19) into master (ecececd) will decrease coverage by 0.33%.
The diff coverage is 56.96%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #317      +/-   ##
==========================================
- Coverage   75.92%   75.58%   -0.34%     
==========================================
  Files          13       13              
  Lines        4299     4350      +51     
==========================================
+ Hits         3264     3288      +24     
- Misses        798      819      +21     
- Partials      237      243       +6     

[goccy]

Thank you for the great PR ! LGTM !