Fix panic with debug_http_headers
Fix panic with debug_http_headers

--- a/doh-client/client.go
+++ b/doh-client/client.go
@@ -223,9 +223,11 @@
 		panic("Unknown request Content-Type")
 	}
 
-	for _, header := range c.conf.DebugHTTPHeaders {
-		if value:= req.response.Header.Get(header); value != "" {
-			log.Printf("%s: %s\n", header, value)
+	if req.response != nil {
+		for _, header := range c.conf.DebugHTTPHeaders {
+			if value := req.response.Header.Get(header); value != "" {
+				log.Printf("%s: %s\n", header, value)
+			}
 		}
 	}
 	if req.err != nil {

--- a/doh-server/server.go
+++ b/doh-server/server.go
@@ -114,7 +114,7 @@
 	}
 
 	for _, header := range s.conf.DebugHTTPHeaders {
-		if value:= r.Header.Get(header); value != "" {
+		if value := r.Header.Get(header); value != "" {
 			log.Printf("%s: %s\n", header, value)
 		}
 	}