Build issue xcode 5 OpenGLImageType FIX

Hello,

I found out a compiling issue using xcode 5 and fixed it

File: juce_OpenGLImage.cpp

Method: OpenGLImageType::create (L182)

FIX:

----------------------------------------------------
if (! im->initialise())

  return nullptr; // should be "return ImagePixelData::Ptr();"

----------------------------------------------------

Thanks

How odd.. I'd have expected that to work just fine. Ah well, thanks!