Minor optimizations in if() blocks

[Ayesh]

A PR with a few micro-optimizations for performance and readability.

1. if() expression order

Expressions in if() are run left-to-right, and evaluating computationally smaller expressions can improve the performance a little bit. This PR contains two of such improvements where it puts === null call and a truthy evaluation ahead of function calls.

2. if()-elseif()-else branching optimizations.

If such a block returns something, the execution of that function is complete, so we often do not need elseif or else blocks. While they don't provide any performance benefit, we take nested code outside, which reduces the cognitive load on developers.

[coveralls]

Coverage remained the same at 100.0% when pulling d5a3f35 on Ayesh:if-branching into b66a2d8 on slimphp:4.x.

[l0gicgate]

Hey thanks for this PR @Ayesh! I suppose there is probably quite of a few instances of this throughout all the codebases. I’m a bit surprised that static analysis doesn’t notify us of those.

[Ayesh]

Thanks a lot @l0gicgate :)
I will see for more similar optimizations and send a PR. Most of the elseif blocks are easy to refactor and remove the besting without affecting anything else.

I also sent slimphp/Slim-Csrf#116 and an update to it if you could kindly take a look. Thank you.