Fix duplicate separator on empty description/url (discord). Fixes #1008 (#1035)

Make this work for all possible cases.
Add tests

bridge/discord/handlers_test.go

@@ -0,0 +1,58 @@
+package bdiscord
+
+import (
+	"testing"
+
+	"github.com/matterbridge/discordgo"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestHandleEmbed(t *testing.T) {
+	testcases := map[string]struct {
+		embed  *discordgo.MessageEmbed
+		result string
+	}{
+		"allempty": {
+			embed:  &discordgo.MessageEmbed{},
+			result: "",
+		},
+		"one": {
+			embed: &discordgo.MessageEmbed{
+				Title: "blah",
+			},
+			result: "embed: blah\n",
+		},
+		"two": {
+			embed: &discordgo.MessageEmbed{
+				Title:       "blah",
+				Description: "blah2",
+			},
+			result: "embed: blah - blah2\n",
+		},
+		"three": {
+			embed: &discordgo.MessageEmbed{
+				Title:       "blah",
+				Description: "blah2",
+				URL:         "blah3",
+			},
+			result: "embed: blah - blah2 - blah3\n",
+		},
+		"twob": {
+			embed: &discordgo.MessageEmbed{
+				Description: "blah2",
+				URL:         "blah3",
+			},
+			result: "embed: blah2 - blah3\n",
+		},
+		"oneb": {
+			embed: &discordgo.MessageEmbed{
+				URL: "blah3",
+			},
+			result: "embed: blah3\n",
+		},
+	}
+
+	for name, tc := range testcases {
+		assert.Equalf(t, tc.result, handleEmbed(tc.embed), "Testcases %s", name)
+	}
+}