Query: Discard non-scalar 'm' instead of attempting to sanitize.

`WP_Query` discards most non-array date values ('year', 'monthnum', etc) by
casting to integer. Since [25138], the 'm' parameter has been handled
as a string; see #24884. However, the string-handling introduced in [25138]
blindly attempted to handle arrays and other non-scalar types as strings,
resulting in PHP notices and invalid MySQL syntax.

Props vortfu.
Fixes #36718.

git-svn-id: https://develop.svn.wordpress.org/trunk@37324 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/query/date.php

@@ -258,6 +258,18 @@ class Tests_Query_Date extends WP_UnitTestCase {
 		$this->assertEquals( $expected_dates, wp_list_pluck( $posts, 'post_date' ) );
 	}
 
+	/**
+	 * @ticket 36718
+	 */
+	public function test_non_scalar_m_should_be_discarded() {
+		$expected = $this->_get_query_result( );
+		$posts    = $this->_get_query_result( array(
+			'm' => array( '1234' ), // ignored
+		) );
+
+		$this->assertEquals( $expected, $posts );
+	}
+
 	public function test_simple_monthnum_expecting_results() {
 		$posts = $this->_get_query_result( array(
 			'monthnum' => 5,