!944 修复StrUtil.split切分长度为0时的bug

Merge pull request !944 from emptypoint/fix-StrUtil.split

hutool-core/src/main/java/cn/hutool/core/text/finder/LengthFinder.java

@@ -19,6 +19,7 @@ public class LengthFinder extends TextFinder {
 	 * @param length 长度
 	 */
 	public LengthFinder(int length) {
+		Assert.isTrue(length > 0, "Length must be great than 0");
 		this.length = length;
 	}
 

hutool-core/src/test/java/cn/hutool/core/util/StrUtilTest.java

@@ -70,6 +70,9 @@ public class StrUtilTest {
 
 		final String[] strings = StrUtil.splitToArray("abc/", '/');
 		Assert.assertEquals(2, strings.length);
+
+		// issue:I6FKSI
+		Assert.assertThrows(IllegalArgumentException.class, () -> StrUtil.split("test length 0", 0));
 	}
 
 	@Test