 Fix build on native MacOSX  (#1207)
 Fix build on native MacOSX  (#1207)

* Fix build on native MacOSX

In cbc2e5 a bug got introduced while trying to special cases
for Qt >= 5.2

* Use c++11 nullptr literal

Justaphf/BitcoinUnlimited,Justaphf/BitcoinUnlimited,BitcoinUnlimited/BitcoinUnlimited,BitcoinUnlimited/BitcoinUnlimited,Justaphf/BitcoinUnlimited,BitcoinUnlimited/BitcoinUnlimited,BitcoinUnlimited/BitcoinUnlimited,Justaphf/BitcoinUnlimited,Justaphf/BitcoinUnlimited,BitcoinUnlimited/BitcoinUnlimited,BitcoinUnlimited/BitcoinUnlimited,Justaphf/BitcoinUnlimited