Update select2.js

Adding case to fix placeholder not being displayed when element not visible.

Author: crueber

select2.js

@@ -2210,6 +2210,11 @@ the specific language governing permissions and limitations under the Apache Lic
             if (searchWidth < 40) {
                 searchWidth = maxWidth - sideBorderPadding;
             }
+            
+            if (searchWidth <= 0) {
+              searchWidth = minimumWidth
+            }
+            
             this.search.width(searchWidth);
         },