Fix crash if an avatar is missing from the server

Which basically never happens.

src/gui/interface/AvatarButton.cpp

@@ -27,8 +27,15 @@ void AvatarButton::Tick(float dt)
 	}
 
 	if (imageRequest && imageRequest->CheckDone())
+	{
+		try
 		{
 			avatar = imageRequest->Finish();
+		}
+		catch (const http::RequestError &ex)
+		{
+			// Nothing, oh well.
+		}
 		imageRequest.reset();
 	}
 }