fix: not using the default template when the custom template does not exist

[guqing]

What type of PR is this?

/kind bug
/area core
/milestone 2.10.x

What this PR does / why we need it:

修复文章自定义模板不存在时没有使用默认模板的问题

see #4617 for more details.

Which issue(s) this PR fixes:

Fixes #4617

Does this PR introduce a user-facing change?

修复文章自定义模板不存在时没有使用默认模板的问题

[guqing]

/cherry-pick release-2.9

[halo-dev-bot]

@guqing: once the present PR merges, I will cherry-pick it on top of release-2.9 in a new PR and assign it to you.

In response to this:

/cherry-pick release-2.9

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[codecov]

Codecov Report

Merging #4618 (ea4d725) into main (da2d56e) will increase coverage by 0.06%.
Report is 9 commits behind head on main.
The diff coverage is 91.66%.

@@             Coverage Diff              @@
##               main    #4618      +/-   ##
============================================
+ Coverage     61.04%   61.11%   +0.06%     
- Complexity     2566     2571       +5     
============================================
  Files           374      374              
  Lines         13168    13173       +5     
  Branches        938      939       +1     
============================================
+ Hits           8039     8051      +12     
+ Misses         4676     4669       -7     
  Partials        453      453              

Files Changed	Coverage Δ
...va/run/halo/app/theme/router/ViewNameResolver.java	85.71% <91.66%> (+2.38%)	⬆️

... and 1 file with indirect coverage changes

[ruibaby]

/lgtm

[JohnNiang]

/lgtm

[JohnNiang]

/lgtm

[f2c-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: JohnNiang

The full list of commands accepted by this bot can be found here.

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Needs approval from an approver in each of these files:

• OWNERS [JohnNiang]

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[halo-dev-bot]

@guqing: new pull request created: #4648

In response to this:

/cherry-pick release-2.9

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.