fix translate warning when widget_prefix and widget_suffix are empty

Author: m-nagai

Resources/views/Form/fields.html.twig

@@ -543,7 +543,7 @@
     {% if 'tab' in form.vars.block_prefixes %}
         {{ block('form_tab') }}
     {% elseif embed_form is sameas(true) %}
-        {{ widget_prefix|trans({}, translation_domain)|raw }} {{ form_widget(form, _context) }} {{ widget_suffix|trans({}, translation_domain)|raw }}
+        {% if widget_prefix is not empty %}{{ widget_prefix|trans({}, translation_domain)|raw }}{% endif %} {{ form_widget(form, _context) }} {% if widget_suffix is not empty %}{{ widget_suffix|trans({}, translation_domain)|raw }}{% endif %}
     {% else %}
         {{ block('widget_form_group_start') }}
 
@@ -557,7 +557,7 @@
         <div class="{{ horizontal_input_wrapper_class }}">
         {% endif %}
 
-        {{ widget_prefix|trans({}, translation_domain)|raw }} {{ form_widget(form, _context) }} {{ widget_suffix|trans({}, translation_domain)|raw }}
+        {% if widget_prefix is not empty %}{{ widget_prefix|trans({}, translation_domain)|raw }}{% endif %} {{ form_widget(form, _context) }} {% if widget_suffix is not empty %}{{ widget_suffix|trans({}, translation_domain)|raw }}{% endif %}
 
         {% set type = type|default('text') %}
         {% if type != 'hidden' %}