fix: Fix a possible crash when parsing RBAC

[jannfis]

PR fixes a possible crash when parsing invalid RBAC policies.

OSS-Fuzz: https://oss-fuzz.com/testcase-detail/6266304514883584

/cc @terrytangyuan @AdamKorcz @hblixt

Signed-off-by: jannfis jann@mistrust.net

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• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this does not need to be in the release notes.
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[AdamKorcz]

For info @DavidKorczynski

[alexmt]

LGTM

[codecov]

Codecov Report

Merging #8165 (72e5df8) into master (5e6aee5) will increase coverage by 0.00%.
The diff coverage is 50.00%.

@@           Coverage Diff            @@
##           master    #8165    +/-   ##
========================================
  Coverage   41.52%   41.53%            
========================================
  Files         174      174            
  Lines       22755    22629   -126     
========================================
- Hits         9450     9399    -51     
+ Misses      11961    11897    -64     
+ Partials     1344     1333    -11     

Impacted Files	Coverage Δ
util/rbac/rbac.go	76.47% <50.00%> (-0.03%)	⬇️
server/application/application.go	31.20% <0.00%> (-1.45%)	⬇️
reposerver/repository/repository.go	57.80% <0.00%> (-0.84%)	⬇️

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