Fix invalid string input (#253)

Signed-off-by: Arthur Chan <arthur.chan@adalogics.com>
Co-authored-by: Guillaume Nodet <gnodet@gmail.com>

Author: arthurscchan

src/main/java/org/fusesource/jansi/AnsiRenderer.java

@@ -99,6 +99,11 @@ public static Appendable render(final String input, Appendable target) throws IO
                 return target;
             }
             j += BEGIN_TOKEN_LEN;
+
+            // Check for invalid string with END_TOKEN before BEGIN_TOKEN
+            if (k < j) {
+                throw new IllegalArgumentException("Invalid input string found.");
+            }
             String spec = input.substring(j, k);
 
             String[] items = spec.split(CODE_TEXT_SEPARATOR, 2);

src/test/java/org/fusesource/jansi/AnsiRendererTest.java

@@ -24,14 +24,14 @@
 import static org.fusesource.jansi.AnsiRenderer.*;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 /**
  * Tests for the {@link AnsiRenderer} class.
  *
  */
 public class AnsiRendererTest {
-
     @BeforeAll
     static void setUp() {
         Ansi.setEnabled(true);
@@ -112,6 +112,11 @@ public void testRenderInvalidMissingEnd() {
         assertEquals("@|bold foo", str);
     }
 
+    @Test
+    public void testRenderInvalidEndBeforeStart() {
+        assertThrows(IllegalArgumentException.class, () -> render("@|@"));
+    }
+
     @Test
     public void testRenderInvalidMissingText() {
         String str = render("@|bold|@");