fix: check allowedList size in StakeAuthorization.Accept

[dudong2]

Description

Currently, only one of AllowedList and DenyList can be set in the structure of StakeAuthorization.
There is a structural problem that causes Accept func to always fail when DenyList is set.
Check the size of the AllowedList together with the isValidatorExists check.

ref. cosmos/cosmos-sdk#11391

closes: #725

Motivation and context

How has this been tested?

Screenshots (if appropriate):

Checklist:

• I followed the contributing guidelines and code of conduct.
• I have added a relevant changelog to CHANGELOG.md
• I have added tests to cover my changes.
• I have updated the documentation accordingly.
• I have updated API documentation client/docs/swagger-ui/swagger.yaml

[codecov]

Codecov Report

Merging #726 (06964c1) into main (00ab960) will increase coverage by 0.00%.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #726   +/-   ##
=======================================
  Coverage   61.89%   61.89%           
=======================================
  Files         874      874           
  Lines       98638    98638           
=======================================
+ Hits        61048    61053    +5     
+ Misses      33966    33957    -9     
- Partials     3624     3628    +4     

Impacted Files	Coverage Δ
x/staking/types/authz.go	87.00% <100.00%> (ø)
x/collection/msgs.go	35.37% <0.00%> (-1.30%)	⬇️
x/token/msgs.go	34.51% <0.00%> (+6.09%)	⬆️