Don't parse empty 'tax_input' keys in edit_post().

This fixes a bug introduced in [31359] where saving a tax_input that contained
only whitespace would result in a random tag being erroneously added to the
post.

See #30615.

git-svn-id: https://develop.svn.wordpress.org/trunk@31392 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/post.php

@@ -337,6 +337,11 @@ function edit_post( $post_data = null ) {
 
 			$clean_terms = array();
 			foreach ( $terms as $term ) {
+				// Empty terms are invalid input.
+				if ( empty( $term ) ) {
+					continue;
+				}
+
 				$_term = get_terms( $taxonomy, array(
 					'name' => $term,
 					'fields' => 'ids',