(fixes issue 392) fix by m.schneider at xabient.de, NSGraphicsContext _currentContext() nil checks
(fixes issue 392) fix by m.schneider at xabient.de, NSGraphicsContext _currentContext() nil checks

gemu2015/cocotron-sierra,JackLian/cocotron,JackLian/cocotron,plasq/cocotron,yuhangwang/cocotron,guestOS/guestOS,Suninus/cocotron,crystax/android-vendor-cocotron,cneira/cocotron,gemu2015/cocotron-sierra,cyclaero/cocotron,crystax/android-vendor-cocotron,cjwl/cocotron,cjwl/cocotron,yuhangwang/cocotron,crystax/android-vendor-cocotron,ruppmatt/cocotron,plasq/cocotron,guestOS/guestOS,guestOS/guestOS,JackLian/cocotron,yuhangwang/cocotron,plasq/cocotron,ruppmatt/cocotron,Suninus/cocotron,JackLian/cocotron,cjwl/cocotron,ruppmatt/cocotron,yuhangwang/cocotron,cneira/cocotron,Suninus/cocotron,plasq/cocotron,gemu2015/cocotron-sierra,cjwl/cocotron,cyclaero/cocotron,guestOS/guestOS,cneira/cocotron,Suninus/cocotron,ruppmatt/cocotron,gemu2015/cocotron-sierra,crystax/android-vendor-cocotron,cyclaero/cocotron,cneira/cocotron,cyclaero/cocotron