UI can block connection to any network if one fails

[wbt]

Describe the bug
Issue #5609 was closed (and I cannot reopen) as a duplicate of Issue #3776 which was supposed to have been addressed by PR# 5893, but the core problem in Issue #5609 still exists. When MetaMask can't connect to the last network it was connected to, it has an overlay that blocks UI functionality that would allow a user to gracefully recover from the situation.

To Reproduce
Steps to reproduce the behavior:

1. Open a browser with MetaMask and log in.

2. In the Network selector, choose Custom RPC.

3. Enter a URL for a network you cannot connect to. For example, http://127.0.1.1:7545.

4. Click Save.

5. MetaMask will attempt to connect, fail, and show a screen like this:
   

6. Click on Switch Networks.

7. Click on Custom RPC.

Expected behavior
Have the same UI as the start of step 3, and be able to enter the correct URL.

Actual behavior
Have the same UI as the start of step 6, and you cannot enter a custom RPC URL.

Workarounds
A: If you happen to have the capacity to bring up an Ethereum network RPC interface at the URL you erroneously specified, you can do that, then Try Again to make a successful connection there, and then go back into the network selector for Custom RPC and enter the URL you intended.

B: If you happen to have capacity to connect to one of the networks already in the network selector list, such as the Main Ethereum Network, you can click on that and make a successful connection, then go back into the network selector for Custom RPC and enter the URL you intended.

In some situations, neither A nor B are feasible options. You can try logging out or restarting the browser, but then you're still unable to recover, as described in the original report at Issue #5609, and arguably in a worse position of not being able to easily log in again.

Browser details (please complete the following information):

• OS: Windows 10 Pro
• Browser: Chrome 72.0.3626.121 (Official Build) (64-bit)
• MetaMask Version: 6.3.1

[github-actions]

This issue has been automatically marked as stale because it has not had recent activity in the last 90 days. It will be closed in 45 days if there is no further activity. The MetaMask team intends on reviewing this issue before close, and removing the stale label if it is still a bug. We welcome new comments on this issue. We do not intend on closing issues if they report bugs that are still reproducible. Thank you for your contributions.

[wbt]

I don't think this should be closed without an improvement.

[github-actions]

This issue has been automatically marked as stale because it has not had recent activity in the last 90 days. It will be closed in 45 days if there is no further activity. The MetaMask team intends on reviewing this issue before close, and removing the stale label if it is still a bug. We welcome new comments on this issue. We do not intend on closing issues if they report bugs that are still reproducible. Thank you for your contributions.

[wbt]

I still don't think this should be closed without an improvement.

[github-actions]

This issue has been automatically marked as stale because it has not had recent activity in the last 90 days. It will be closed in 45 days if there is no further activity. The MetaMask team intends on reviewing this issue before close, and removing the stale label if it is still a bug. We welcome new comments on this issue. We do not intend on closing issues if they report bugs that are still reproducible. Thank you for your contributions.

[github-actions]

This issue was closed because there has been no follow up activity in the last 45 days. If you feel this was closed in error, please reopen and provide evidence on the latest release of the extension. Thank you for your contributions.