Never disable network form save button if props chain ID is invalid

[rekmarks]

We received reports of users trying to update the chain ID for custom networks but the save button being disabled. This could happen if they had correctly stored the chain ID in decimal prior to version 8.1 of the extension.

In that case, we'd flag the network as invalid, and prompt the user to change it. However, if they re-entered the same decimal value, the form would disable the save button, since it compared the entered chain ID value against persisted chain ID value.

This PR avoids this problem by never flagging the form state as "unchanged" if the persisted chain ID is invalid.

[Gudahtt]

This needs to be rebased to fix the linter (I introduced a lint error that was then fixed in #9806)

[metamaskbot]

Builds ready [929a140]

• builds: chrome, firefox, opera
• bundle viz: background, ui, inpage, contentscript, ui-libs, bg-libs, phishing-detect
• dep viz: background
• all artifacts

Page Load Metrics (392 ± 62 ms)

Platform	Page	Metric	Min (ms)	Max (ms)	Average (ms)	StandardDeviation (ms)	MarginOfError (ms)
Chrome	Home	firstPaint	30	54	36	5	3
		domContentLoaded	256	719	391	129	62
		load	257	720	392	129	62
		domInteractive	255	718	391	129	62

[Gudahtt]

LGTM!