HTML API: Remove superfluous type-coercing empty() check.

When returning modifiable text in the HTML API, if the text segment
coerces to `false` inside `empty()`, then an empty string has been
returned instead of the string itself. For example, the text node in the
following HTML snippet:

{{{
    <div>0</div>
}}}

In this patch the `empty()` check is removed. The purpose of the original
check was to skip further processing if the text content is empty, but
the check is not needed and the additioanl processing is minimal.
Removing the code removes the defect and leaves a cleaner method in its
absence.

Developed in #6199

Follow-up to [57348]
Follow-up to #60170



git-svn-id: https://develop.svn.wordpress.org/trunk@57738 602fd350-edb4-49c9-b593-d223f7449a82

Author: dmsnell

src/wp-includes/html-api/class-wp-html-tag-processor.php

@@ -2810,10 +2810,6 @@ public function get_modifiable_text() {
 
 		$decoded = html_entity_decode( $text, ENT_QUOTES | ENT_HTML5 | ENT_SUBSTITUTE );
 
-		if ( empty( $decoded ) ) {
-			return '';
-		}
-
 		/*
 		 * TEXTAREA skips a leading newline, but this newline may appear not only as the
 		 * literal character `\n`, but also as a character reference, such as in the