jruby: Pass end index to byteListToInum (#150)

These parse methods take begin and end indices, not begin and length. A
test is included.

Fixes jruby/jruby#8823

Author: headius

ext/jruby/org/jruby/ext/strscan/RubyStringScanner.java

@@ -651,7 +651,7 @@ private RubyInteger strscanParseInteger(Ruby runtime, ByteList bytes, int ptr, i
         setMatched();
         adjustRegisters();
 
-        return ConvertBytes.byteListToInum(runtime, bytes, ptr, len, base, true);
+        return ConvertBytes.byteListToInum(runtime, bytes, ptr, ptr + len, base, true);
     }
 
     private void strscanMustAsciiCompat(Ruby runtime) {

test/strscan/test_stringscanner.rb

@@ -1006,6 +1006,12 @@ def test_scan_integer
     assert_equal(huge_integer.to_i, s.scan_integer)
     assert_equal(2_000, s.pos)
     assert_predicate(s, :matched?)
+
+    s = create_string_scanner('abc1')
+    s.pos = 3
+    assert_equal(1, s.scan_integer)
+    assert_equal(4, s.pos)
+    assert_predicate(s, :matched?)
   end
 
   def test_scan_integer_unmatch