fix(core): harden to-lines typecheck

Author: marionebl

Diff for: @commitlint/core/src/library/to-lines.js

@@ -1,5 +1,5 @@
 export default function toLines(input) {
-	if (typeof input === 'undefined') {
+	if (typeof input !== 'string') {
 		return [];
 	}
 

Diff for: @commitlint/core/src/library/to-lines.test.js

@@ -5,7 +5,7 @@ test('should return an array for empty input', t => {
 	t.deepEqual(toLines(), []);
 });
 
-test.failing('should return an array for null input', t => {
+test('should return an array for null input', t => {
 	t.deepEqual(toLines(null), []);
 });
 

Diff for: @commitlint/core/src/rules/footer-leading-blank.test.js

@@ -78,13 +78,13 @@ test('with trailing message should succeed for "always"', async t => {
 	t.is(actual, expected);
 });
 
-test.failing('without body should succeed for "never"', async t => {
+test('without body should fail for "never"', async t => {
 	const [actual] = footerLeadingBlank(await parsed.withoutBody, 'never');
-	const expected = true;
+	const expected = false;
 	t.is(actual, expected);
 });
 
-test.failing('without body should succeed for "always"', async t => {
+test('without body should succeed for "always"', async t => {
 	const [actual] = footerLeadingBlank(await parsed.withoutBody, 'always');
 	const expected = true;
 	t.is(actual, expected);