[FIX] web: Fix the height of svg when signature is empty

Currently, in the user setting, hovering on the live chat input will
focus on the signature div due to long height of the empty svg.

So in this commit fixes the issue by adding the css property in the
svg element of signature widget due to that svg element contains the
proper width and height.

closes odoo/odoo#61897

Taskid: 2361880
X-original-commit: 6fe2a0b8b6f8dadb2eb7008019f2d7266dcf6fb1
Signed-off-by: Yannick Tivisse (yti) <yti@odoo.com>

addons/web/static/src/scss/name_and_signature.scss

@@ -26,6 +26,9 @@
     .o_signature {
         outline: 1px solid rgba(theme-color('secondary'), 0.3);
         position: relative;
+        &.o_signature_empty {
+            display: flex;
+        }
         > p {
             position: absolute;
             top: 50%;