fix crash when OpenGL view size goes negative, (context w/h limited to 0,0)
fix crash when OpenGL view size goes negative, (context w/h limited to 0,0)

liruqi/cocotron,mpw/marcelweiher-libobjc2,berkus/cocotron,uptime-services/development-arts,mpw/marcelweiher-libobjc2,berkus/cocotron,uptime-services/development-arts,liruqi/cocotron,liruqi/cocotron,mpw/marcelweiher-libobjc2,liruqi/cocotron,uptime-services/development-arts,uptime-services/development-arts,mpw/marcelweiher-libobjc2,berkus/cocotron,berkus/cocotron