git-town panics if you have additional remotes

[bryanlarsen]

Steps to reproduce

git remote add foo <url>
git town sync

Command output

panic: unknown remote: "foo"

goroutine 1 [running]:
github.com/git-town/git-town/v14/src/git/gitdomain.NewRemote({0xc00002b308, 0xa})
        D:/a/git-town/git-town/src/git/gitdomain/remote.go:14 +0xe5
github.com/git-town/git-town/v14/src/git/gitdomain.NewRemotes({0xc001b2fda0, 0x2, 0xd9ff20?})
        D:/a/git-town/git-town/src/git/gitdomain/remotes.go:13 +0x70
github.com/git-town/git-town/v14/src/git.(*BackendCommands).RemotesUncached(0xc00007d440)
        D:/a/git-town/git-town/src/git/backend_commands.go:364 +0xf0
github.com/git-town/git-town/v14/src/git.(*BackendCommands).Remotes(0xc00007d440)
        D:/a/git-town/git-town/src/git/backend_commands.go:346 +0x25
github.com/git-town/git-town/v14/src/execute.LoadRepoSnapshot({0xc0001dac18, {0x1325c20, 0x0, 0x0}, 0x1, 0x1, 0xc0001bb6e0, {0x0, 0x1, 0x0, ...}, ...})
        D:/a/git-town/git-town/src/execute/load_repo_snapshot.go:49 +0x3af
github.com/git-town/git-town/v14/src/cmd.determineSyncConfig(0x0, 0xc0001bb6e0, 0x0)
        D:/a/git-town/git-town/src/cmd/sync.go:138 +0x1b8
github.com/git-town/git-town/v14/src/cmd.executeSync(0x0, 0x0, 0x0)
        D:/a/git-town/git-town/src/cmd/sync.go:72 +0xae
github.com/git-town/git-town/v14/src/cmd.syncCmd.func1(0xc0001da008, {0x1325c20?, 0x4?, 0xca7d75?})
        D:/a/git-town/git-town/src/cmd/sync.go:51 +0x66
github.com/spf13/cobra.(*Command).execute(0xc0001da008, {0x1325c20, 0x0, 0x0})
        D:/a/git-town/git-town/vendor/github.com/spf13/cobra/command.go:983 +0xaca
github.com/spf13/cobra.(*Command).ExecuteC(0xc0001aa308)
        D:/a/git-town/git-town/vendor/github.com/spf13/cobra/command.go:1115 +0x3ff
github.com/spf13/cobra.(*Command).Execute(...)
        D:/a/git-town/git-town/vendor/github.com/spf13/cobra/command.go:1039
github.com/git-town/git-town/v14/src/cmd.Execute()
        D:/a/git-town/git-town/src/cmd/core.go:38 +0x619
main.main()
        D:/a/git-town/git-town/main.go:18 +0x1e

### Additional information

Git Town 14.1.0