Fix index out of bounds when escaping strings

Author: steve-s

graalpython/com.oracle.graal.python.test/src/com/oracle/graal/python/test/parser/StringUtilsTests.java

@@ -82,6 +82,7 @@ public void blockCjkUnifiedIdeographUnknownCharacters() throws Exception {
 
     @Test
     public void malformedError() throws Exception {
+        checkSyntaxErrorMessage("'\\N'", "SyntaxError: (unicode error) 'unicodeescape' codec can't decode bytes in position 0-1: malformed \\N character escape");
         checkSyntaxErrorMessage("'\\N {LATIN CAPITAL LETTER A}'", "SyntaxError: (unicode error) 'unicodeescape' codec can't decode bytes in position 0-1: malformed \\N character escape");
         checkSyntaxErrorMessage("'\\N LATIN CAPITAL LETTER A}'", "SyntaxError: (unicode error) 'unicodeescape' codec can't decode bytes in position 0-1: malformed \\N character escape");
         checkSyntaxErrorMessage("'\\N{LATIN CAPITAL LETTER A'", "SyntaxError: (unicode error) 'unicodeescape' codec can't decode bytes in position 0-24: malformed \\N character escape");

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/parser/sst/StringUtils.java

@@ -206,6 +206,9 @@ public static String unescapeJavaString(String st) {
      */
     @CompilerDirectives.TruffleBoundary
     private static int doCharacterName(String text, StringBuilder sb, int offset) {
+        if (offset >= text.length()) {
+            throw PythonLanguage.getCore().raise(PythonBuiltinClassType.UnicodeDecodeError, UNICODE_ERROR + MALFORMED_ERROR, offset - 2, offset - 1);
+        }
         char ch = text.charAt(offset);
         if (ch != '{') {
             throw PythonLanguage.getCore().raise(PythonBuiltinClassType.UnicodeDecodeError, UNICODE_ERROR + MALFORMED_ERROR, offset - 2, offset - 1);