fix: panic when the token is malformed

[sibicramesh]

NOTE: This fix only avoids the crash. This doesn't explain why the token was messed up in the first place.

The issue here is the signature position in the token is missing and the check for that was absent. We then proceed to extract the signature from this position in this case will be 0. So is this panic

panic: runtime error: slice bounds out of range [22:0]

Added unit tests to avoid regression.

Full stack here enforcerd.log

[sibicramesh]

/build - automatically fired by gogo with following PRs and commit SHAs v1.0.0

[
  {
    "project": "",
    "component": "enforcerd",
    "pr-id": "1551",
    "commit-sha": "dc8842341f71ce64692c8184b81a3a97bca94403",
    "pipeline": "master"
  },
  {
    "project": "",
    "component": "trireme-lib",
    "pr-id": "951",
    "commit-sha": "9cbbc4d1b9c17c5ba77bca07c0b623d79c09e536",
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[codecov[bot]]

Codecov Report

Merging #951 into master will increase coverage by 0.05%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #951      +/-   ##
==========================================
+ Coverage   54.87%   54.92%   +0.05%     
==========================================
  Files         123      123              
  Lines       11735    11735              
==========================================
+ Hits         6439     6445       +6     
+ Misses       4674     4671       -3     
+ Partials      622      619       -3

Impacted Files	Coverage Δ
controller/pkg/tokens/binaryjwt.go	63.39% <100%> (+2.67%)	:arrow_up:

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