Ignore only the malformed _redirects/_headers rules.

Before this commit, upon encountering a malformed rule, the entire file
was ignored. This is both increasingly unviable for complex sites,
a likely source of self-DoS (or at least degradation of service),
and not the behavior Grebedoc has been promising for a few weeks.

src/headers.go

@@ -103,8 +103,9 @@ func ProcessHeadersFile(manifest *Manifest) error {
 
 	for index, rule := range rules {
 		if err := validateHeaderRule(rule); err != nil {
-			return AddProblem(manifest, headersFileName,
+			AddProblem(manifest, headersFileName,
 				"rule #%d %q: %s", index+1, rule.Path, err)
+			continue
 		}
 		headerMap := []*Header{}
 		for header, values := range rule.Headers {

src/redirects.go

@@ -102,8 +102,9 @@ func ProcessRedirectsFile(manifest *Manifest) error {
 
 	for index, rule := range rules {
 		if err := validateRedirectRule(rule); err != nil {
-			return AddProblem(manifest, redirectsFileName,
+			AddProblem(manifest, redirectsFileName,
 				"rule #%d %q: %s", index+1, unparseRule(rule), err)
+			continue
 		}
 		manifest.Redirects = append(manifest.Redirects, &RedirectRule{
 			From:   proto.String(rule.From),