fix(qrgen): fix "trim spaces" checkbox hold state over submits

Only use submitted data to populate form when in POST handler.
Otherwise default value for Boolean field gets clobbered.

app/templates/main.html

@@ -15,7 +15,7 @@
 
 	<div> {{ form.user_data }} </div>
 	<div class="input submit">
-		{{ form.trim_spaces(checked=True) }} {{ form.trim_spaces.label }}
+		{{ form.trim_spaces }} {{ form.trim_spaces.label }}
 		{{ form.submit }} </div>
 </form>
 </p>