Always cast term_ids as integers.

Passing term IDs to WP as strings results in WP
making new terms. For existing terms, always cast
the ID as an integer to avoid this issue (and to
ensure a match).

class-wxr-importer.php

@@ -2319,18 +2319,18 @@ protected function term_exists( $data ) {
 
 		// Constant-time lookup if we prefilled
 		if ( $this->options['prefill_existing_terms'] ) {
-			return isset( $this->exists['term'][ $exists_key ] ) ? $this->exists['term'][ $exists_key ] : false;
+			return isset( $this->exists['term'][ $exists_key ] ) ? (int) $this->exists['term'][ $exists_key ] : false;
 		}
 
 		// No prefilling, but might have already handled it
 		if ( isset( $this->exists['term'][ $exists_key ] ) ) {
-			return $this->exists['term'][ $exists_key ];
+			return (int) $this->exists['term'][ $exists_key ];
 		}
 
 		// Still nothing, try WP's term_exists, and cache it.
 		$exists = term_exists( $data['slug'], $data['taxonomy'] );
 		if ( is_array( $exists ) ) {
-			$exists = $exists['term_id'];
+			$exists = (int) $exists['term_id'];
 		}
 
 		$this->exists['term'][ $exists_key ] = $exists;