[FIX] _enoughSpaceBelow + Avoids duplicate calls of functions

Hello!

As a heavy user and lover of this plugin, I decided to fix some problems in the current development version (1.1).

• Changed the _enoughSpaceBelow _enoughSpace (checking both possibilities targeting to open the drop-down menu above or below)
• Avoid duplicate calls of functions (as _openDropdown and _enoughSpaceBelow)

Hope I helped, and still intend to keep correcting other problems.