Expand input-group of Many2One when readonly and empty

issue6763
review38691002

src/sao.less

@@ -149,6 +149,9 @@ button {
             height: 1em;
         }
     }
+    & .form-many2one > .input-group {
+        width: 100%;
+    }
     & td.form-one2many, td.form-many2many {
         vertical-align: top;
     }