plugins: Fix panic with /health and envoy plugin

If there was a nil status value it was still being added to the
status map, but the server didn't check before dereferencing it.

We now just check if the pointer is nil before trying to use it.

Fixes: #2396
Signed-off-by: Patrick East <east.patrick@gmail.com>

server/server.go

@@ -1008,7 +1008,7 @@ func (s *Server) unversionedGetHealth(w http.ResponseWriter, r *http.Request) {
 		// Ensure that all plugins (if requested to be included in the result) have an OK status.
 		hasErr := false
 		for _, status := range pluginStatuses {
-			if status.State != plugins.StateOK {
+			if status != nil && status.State != plugins.StateOK {
 				hasErr = true
 				break
 			}

server/server_test.go

@@ -326,7 +326,6 @@ func TestUnversionedGetHealthCheckDiscoveryWithPlugins(t *testing.T) {
 			},
 			exp: 500,
 		},
-
 		{
 			note: "all plugins ready - recovery",
 			statusUpdates: map[string]*plugins.Status{
@@ -336,6 +335,13 @@ func TestUnversionedGetHealthCheckDiscoveryWithPlugins(t *testing.T) {
 			},
 			exp: 200,
 		},
+		{
+			note: "nil plugin status",
+			statusUpdates: map[string]*plugins.Status{
+				"p1": nil,
+			},
+			exp: 200,
+		},
 	}
 
 	for _, tc := range cases {