Upload: Add missing escaping in upload_space_setting().

Follow-up to [https://mu.trac.wordpress.org/changeset/1088 mu:1088], [https://mu.trac.wordpress.org/changeset/1095 mu:1095], [12603].

Props utsav72640.
Fixes #58514.

git-svn-id: https://develop.svn.wordpress.org/trunk@57175 602fd350-edb4-49c9-b593-d223f7449a82

Author: SergeyBiryukov

src/wp-admin/includes/ms.php

@@ -305,7 +305,9 @@ function upload_space_setting( $id ) {
 	<tr>
 		<th><label for="blog-upload-space-number"><?php _e( 'Site Upload Space Quota' ); ?></label></th>
 		<td>
-			<input type="number" step="1" min="0" style="width: 100px" name="option[blog_upload_space]" id="blog-upload-space-number" aria-describedby="blog-upload-space-desc" value="<?php echo $quota; ?>" />
+			<input type="number" step="1" min="0" style="width: 100px"
+				name="option[blog_upload_space]" id="blog-upload-space-number"
+				aria-describedby="blog-upload-space-desc" value="<?php echo esc_attr( $quota ); ?>" />
 			<span id="blog-upload-space-desc"><span class="screen-reader-text">
 				<?php
 				/* translators: Hidden accessibility text. */