fix hasData for non-post requests

the default value of the $data property is an empty array, which for
some encodings would be encoded into a non-empty string. this would
cause hasData to return true even for request types that are not meant
to send data, which again would trigger an if condition that calls
curl_setopt with CURLOPT_POSTFIELDS.

fixes #61

src/Request.php

@@ -337,7 +337,7 @@ public function setData($data)
 	 */
 	public function hasData()
 	{
-		return (bool) $this->encodeData();
+		return static::$methods[$this->method] && (bool) $this->encodeData();
 	}
 
 	/**
@@ -401,7 +401,7 @@ public function encodeData()
 			case static::ENCODING_RAW:
 				return $this->data;
 			default:
-				$msg = "Encoding [" . $this->encoding . "] not a known Request::ENCODING_* constant";
+				$msg = "Encoding [$this->encoding] not a known Request::ENCODING_* constant";
 				throw new \UnexpectedValueException($msg);
 		}
 	}

tests/unit/RequestTest.php

@@ -124,4 +124,14 @@ public function cookies()
 		$this->assertEquals('foo', $r->getCookie('baz'));
 		$this->assertEquals('baz=foo', $r->getHeader('cookie'));
 	}
+
+	/** @test */
+	public function emptyJsonGetRequestHasNoData()
+	{
+		$r = $this->makeRequest();
+		$r->setEncoding(Request::ENCODING_JSON);
+		$r->setMethod('get');
+
+		$this->assertFalse($r->hasData());
+	}
 }