Implement Error Handling for Memory Allocation Functions

[KellyLTran]

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• Version of iperf3 (or development branch, such as master or
  3.1-STABLE) to which this pull request applies:

• Issues fixed (if any):

• Brief description of code changes (suitable for use as a commit message):
  This pull request implements error handling for the memory allocation functions involving the "malloc" and "calloc" functions. Particularly focused on return values for error cases, this pull request clarifies when certain memory allocations do not work, which allows developers to clearly identify mistakes and where the issue is. Error messages are also used for code readability and clarity. This aims to make testing and bug fixing easier and more efficient.

[bmah888]

Thanks for the pull request! Er, did you mean for those Zone.Identifier files to be added?

EDIT: I agree that giving more diagnostic information to help fix flaws are good.

One of the reasons that iperf3 is fairly terse with error messages is that in some places, printing out diagnostics can interfere with JSON output. This isn't the case everywhere but it requires a little thought about how to express additional information such as what you're proposing to do.