fix: mongodb input plugin issue #9845

[howardyoo]

input plugin would fail (and result in seg fault) because there was no check to see if newStat.Metrics.Repl.Network.GetMores was nil or not. Added a checking so that the assignment would happen only when newStat.Metrics.Repl.Network.GetMores is not nil.

Required for all PRs:

• Updated associated README.md.
• Wrote appropriate unit tests.
• Pull request title or commits are in conventional commit format (e.g. feat: or fix:)

resolves influxdata#9845

This code change will make sure to check the newStat.Metrics.Repl.Network.GetMores is not null, before performing any access to its underlying variables. This will prevent the mongodb plugin from resulting into segmentation violation that the issue influxdata#9845 reported.

if newStat.Metrics.Repl.Network.GetMores != nil {
					returnVal.ReplNetworkGetmoresNum = newStat.Metrics.Repl.Network.GetMores.Num
					returnVal.ReplNetworkGetmoresTotalMillis = newStat.Metrics.Repl.Network.GetMores.TotalMillis
				}