feature symfony#24148 [Form] Hide label button when its setted to false (TeLiXj)

This PR was submitted for the 2.7 branch but it was merged into the 3.4 branch instead (closes symfony#24148).

Discussion
----------

[Form] Hide label button when its setted to false

| Q             | A
| ------------- | ---
| Branch?       | 2.7
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | no
| Fixed tickets |
| License       | MIT
| Doc PR        |

Added same behaviour in buttons like in other form components when label is setted to false, don't show it.
It's very useful with buttons with icon and without text.

Commits
-------

e319075 Hide label button when its setted to false

Author: fabpot

src/Symfony/Bridge/Twig/Resources/views/Form/form_div_layout.html.twig

@@ -216,7 +216,7 @@
 {%- endblock range_widget %}
 
 {%- block button_widget -%}
-    {%- if label is empty -%}
+    {%- if label is not same as(false) and label is empty -%}
         {%- if label_format is not empty -%}
             {% set label = label_format|replace({
                 '%name%': name,