fix server from crashing after restart not having user data

src/main/main.go

@@ -94,9 +94,18 @@ func profileHandler(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	_, exists := userData[sessionData.UserID]
+
+	if !exists {
+		logging.Error("Session id exists but user does not exist")
+		http.Redirect(w, r, "/login", http.StatusSeeOther)
+		return
+	}
+
 	if r.Method == http.MethodGet {
 		tmpl := template.Must(template.ParseFiles("src/pages/profile_page.html"))
 		userDataMutex.RLock()
+
 		tmpl.Execute(w, ProfileData{
 			Username:    sessionData.UserID,
 			Email:       userData[sessionData.UserID].Email,