Fix add snapshot page

nummi/main/templates/main/snapshot.html

@@ -32,6 +32,7 @@
 	</div>
 </form>
 
+{% if categories %}
 <h2>Plot</h2>
 <div class="chart">
 	{% for cat in categories %}
@@ -83,6 +84,7 @@
 	</div>
 	{% endfor %}
 </div>
+{% endif %}
 
 {% if snapshot.transactions %}
 <h2>Transactions ({{ sum|pmvalue }} / {{ snapshot.diff|pmvalue }})</h2>