Fix parsing long field values

Fields with > 250 characters were causing problems. See:

http://github.com/felixge/node-mysql/issues#issue/7
http://github.com/felixge/node-mysql/issues#issue/8

lib/mysql/parser.js

@@ -493,7 +493,8 @@ Parser.prototype.write = function(buffer) {
         }
 
         packet.columnLength = lengthCoded(packet.columnLength);
-        if (!packet.columnLength) {
+
+        if (!packet.columnLength && !this._lengthCodedLength) {
           packet.emit('data', (packet.columnLength === null ? null : new Buffer(0)), 0);
           if (packet.received < packet.length) {
             advance(Parser.COLUMN_VALUE_LENGTH);

test/system/test-client-query-long-fields.js

@@ -0,0 +1,42 @@
+require('../common');
+var Client = require('mysql').Client,
+    client = Client(TEST_CONFIG),
+    gently = new Gently();
+
+// our test db might not exist yet, so don't try to connect to it
+client.connect();
+
+function makeString(length) {
+  var str = '';
+  for (var i = 0; i < length; i++) {
+    str += 'x';
+  }
+  return str;
+}
+
+var field_a = makeString(250),
+    field_b = makeString(251),
+    field_c = makeString(512),
+    field_d = makeString(65537);
+
+function test(last) {
+  var query = client.query(
+    'SELECT ? as field_a, ? as field_b, ? as field_c, ? as field_d',
+    [field_a, field_b, field_c, field_d],
+    function(err, results) {
+    if (err) throw err;
+
+    assert.equal(results[0].field_a, field_a);
+    assert.equal(results[0].field_b, field_b);
+    assert.equal(results[0].field_c, field_c);
+    assert.equal(results[0].field_d, field_d);
+    if (last) {
+      client.end();
+    }
+  });
+}
+
+// We execute this test twice to be sure the parser is in a good state after
+// each run.
+test();
+test(true);