proxy/grpcproxy: add return on error for metrics handler

Signed-off-by: Sam Batschelet <sbatsche@redhat.com>

proxy/grpcproxy/metrics.go

@@ -89,6 +89,7 @@ func HandleMetrics(mux *http.ServeMux, c *http.Client, eps []string) {
 		resp, err := c.Get(target)
 		if err != nil {
 			http.Error(w, "Internal server error", http.StatusInternalServerError)
+			return
 		}
 		defer resp.Body.Close()
 		w.Header().Set("Content-Type", "text/plain; version=0.0.4")