Fix avatar urls when there is no avatar

Change-Id: Ifa8bb5d4cdbfd2756d792691210d5cdcb8d47820
diff --git a/server/src/services/ConversationService.ts b/server/src/services/ConversationService.ts
index 5265c16..f844c0c 100644
--- a/server/src/services/ConversationService.ts
+++ b/server/src/services/ConversationService.ts
@@ -57,7 +57,7 @@
       infos: {
         // Build a dataUrl from the avatar
         // TODO: Host the image and use a "normal" url instead
-        avatar: `data:image/jpeg;base64,${jamidRequest.avatar}`,
+        avatar: jamidRequest.avatar ? `data:image/jpeg;base64,${jamidRequest.avatar}` : undefined,
         description: jamidRequest.description,
         mode: jamidRequest.mode,
         title: jamidRequest.title,
@@ -76,7 +76,7 @@
     }
     // Build a dataUrl from the avatar
     // TODO: Host the image and use a "normal" url instead
-    infos.avatar = `data:image/jpeg;base64,${infos.avatar}`;
+    infos.avatar = infos.avatar ? `data:image/jpeg;base64,${infos.avatar}` : undefined;
 
     const membersNames = await this.getMembersNames(accountId, conversationId);
     let lastMessage: Message | undefined;