Fix StringIndexOutOfBoundsException with unclosed inline link (#27)

An example input that caused it: [example.com](http:\\example.com

The code was missing a bounds check. By using peek() we get that, as in
other places.

Also add an integration test that tries to trigger out of bounds by
using substrings of the spec examples.

Author: robinst

commonmark-integration-test/src/test/java/org/commonmark/integration/BoundsIntegrationTest.java

@@ -0,0 +1,61 @@
+package org.commonmark.integration;
+
+import org.commonmark.node.Node;
+import org.commonmark.parser.Parser;
+import org.commonmark.spec.SpecExample;
+import org.commonmark.spec.SpecReader;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.Parameterized;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import static org.junit.Assert.assertNotNull;
+
+/**
+ * Tests various substrings of the spec examples to check for out of bounds exceptions.
+ */
+@RunWith(Parameterized.class)
+public class BoundsIntegrationTest {
+
+    private static final Parser PARSER = Parser.builder().build();
+
+    protected final String input;
+
+    public BoundsIntegrationTest(String input) {
+        this.input = input;
+    }
+
+    @Parameterized.Parameters(name = "{0}")
+    public static List<Object[]> data() {
+        List<SpecExample> examples = SpecReader.readExamples();
+        List<Object[]> data = new ArrayList<>();
+        for (SpecExample example : examples) {
+            data.add(new Object[]{example.getSource()});
+        }
+        return data;
+    }
+
+    @Test
+    public void testSubstrings() {
+        // Check possibly truncated block/inline starts
+        for (int i = 1; i < input.length() - 1; i++) {
+            parse(input.substring(i));
+        }
+        // Check possibly truncated block/inline ends
+        for (int i = input.length() - 1; i > 1; i--) {
+            parse(input.substring(0, i));
+        }
+    }
+
+    private void parse(String input) {
+        try {
+            Node parsed = PARSER.parse(input);
+            // Parsing should always return a node
+            assertNotNull(parsed);
+        } catch (Exception e) {
+            throw new AssertionError("Parsing failed, input: " + input, e);
+        }
+    }
+}

commonmark/src/main/java/org/commonmark/internal/InlineParserImpl.java

@@ -570,7 +570,7 @@ private boolean parseCloseBracket() {
                     title = parseLinkTitle();
                     spnl();
                 }
-                if (input.charAt(index) == ')') {
+                if (peek() == ')') {
                     index++;
                     isLinkOrImage = true;
                 }