Fix autocomplete chip X "ends with" conflicts

Clicking the X button in an autocomplete chip could inadvertently remove
the wrong tag (and cause a weird "merging" behavior) if another tag
ended with the same text as the one being removed. For example, if a
post had both "one.two" and "two" tags and you clicked the X button on
the "two".

tildes/static/js/behaviors/autocomplete-chip-clear.js

@@ -6,7 +6,7 @@ $.onmount("[data-js-autocomplete-chip-clear]", function() {
         var $tagsHiddenInput = $("[data-js-autocomplete-hidden-input]");
         var $autocompleteInput = $("[data-js-autocomplete-input]");
 
-        var textToReplace = new RegExp($chip.text() + ",");
+        var textToReplace = new RegExp("(^|,)" + $chip.text() + ",");
         $tagsHiddenInput.val($tagsHiddenInput.val().replace(textToReplace, ""));
         $chip.remove();
         $autocompleteInput.focus();