cli: Fix init failure with deleted cache

The init command needs to initialize a backend, in order to access
state, in turn to derive provider requirements from state. The backend
initialization step requires building provider factories, which
previously would fail if a lockfile was present without a corresponding
local provider cache.

This commit ensures that in this situation only, errors with the
provider factories are temporarily ignored. This allows us to continue
to initialize the backend, fetch providers, and then report any errors
as necessary.

internal/command/init.go

@@ -238,7 +238,7 @@ func (c *InitCommand) Run(args []string) int {
 		// by a previous run, so we must still expect that "back" may be nil
 		// in code that follows.
 		var backDiags tfdiags.Diagnostics
-		back, backDiags = c.Backend(nil)
+		back, backDiags = c.Backend(&BackendOpts{Init: true})
 		if backDiags.HasErrors() {
 			// This is fine. We'll proceed with no backend, then.
 			back = nil