Fix test for joystick presence in matchCallback

The matchCallback function has an initial loop to filter out redundant
joystick additions based on matching deviceRef values.  However, the if
statement incorrectly combines this test with the condition that the
joystick is not present, which is obviously incorrect.

Closes #753.

src/cocoa_joystick.m

@@ -276,7 +276,7 @@ static void matchCallback(void* context,
 
     for (joy = GLFW_JOYSTICK_1;  joy <= GLFW_JOYSTICK_LAST;  joy++)
     {
-        if (!_glfw.ns_js.js[joy].present && _glfw.ns_js.js[joy].deviceRef == deviceRef)
+        if (_glfw.ns_js.js[joy].present && _glfw.ns_js.js[joy].deviceRef == deviceRef)
             return;
     }