🐛 fix parse ips return invalid in abnormal case

[huykn]

Description

When we call func c.IPs() parse header x-forwarded-for in some case return invalid data
ex:

app := New()
c := app.AcquireCtx(&fasthttp.RequestCtx{})
defer app.ReleaseCtx(c)
c.Request().Header.Set("x-forwarded-for", "1.1.1.1,8.8.8.8 , /n, \n,1.1, a.c, 6.,6., , a,,42.118.81.169,10.0.137.108")
var res string
b.ReportAllocs()
b.ResetTimer()
for n := 0; n < b.N; n++ {
  ips := c.IPs()
  res = ips[len(ips)-2]
}
utils.AssertEqual(b, "42.118.81.169", res) // failed in this case. invalid value return: ,42.118.81.169

Fixes # (issue)

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• For new functionalities I follow the inspiration of the express js framework and built them similar in usage
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation - /docs/ directory for https://docs.gofiber.io/
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• If new dependencies exist, I have checked that they are really necessary and agreed with the maintainers/community (we want to have as few dependencies as possible)
• I tried to make my code as fast as possible with as few allocations as possible
• For new code I have written benchmarks so that they can be analyzed and improved

Commit formatting:

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[ReneWerner87]

@huykn pls check my review comment