configs/configupgrade: Don't panic if analyzer fails

Previously we were trying to access a field of the analysis object before
checking if analysis produced errors. The analysis function usually
returns a nil analysis on error, so this would result in a panic whenever
that happened.

Now we'll dereference the analysis object pointer only after checking for
errors, so we'll get a chance to report the analysis error to the user.

configs/configupgrade/upgrade.go

@@ -35,11 +35,11 @@ func (u *Upgrader) Upgrade(input ModuleSources, dir string) (ModuleSources, tfdi
 	var diags tfdiags.Diagnostics
 
 	an, err := u.analyze(input)
-	an.ModuleDir = dir
 	if err != nil {
 		diags = diags.Append(err)
 		return ret, diags
 	}
+	an.ModuleDir = dir
 
 	for name, src := range input {
 		ext := fileExt(name)