Fix adding empty tag on focus out from element

For some reason, i was looking at the value of the focus’ **target**,
which is not my search field at all, but whatever control the focus
changes **to**.  It that new control is an input with value, then it
created a new tag with whatever my search field had, which could be the
empty string.

web/static/numerus.js

@@ -345,7 +345,7 @@ class Tags extends HTMLDivElement {
             this.search.addEventListener('keydown', this.onSearchKeydownHandler);
             this.onFocusOutHandler = (e) => {
                 if (this.contains(e.target)) return;
-                if (e.target.value && e.target.value.trim() !== '') {
+                if (this.search.value && this.search.value.trim() !== '') {
                     this.createTag();
                 }
             };