Fixed: CPNumberFormatter formatted @"" as any number.
Fixed: CPNumberFormatter formatted @"" as any number.

Without this fix, `- CPNumberFormatter getObjectValue:forString:errorDescription:` would return `YES` for string @"", like if it was properly converted to an object value, but then actually leave object value unchanged.

With this fix object value is set to nil like in Cocoa.

Refs #1829.

rgv151/cappuccino,zittix/cappuccino,FrankReh/cappuccino,FrankReh/cappuccino,wangshijin/cappuccino,enquora/cappuccino,rgv151/cappuccino,FrankReh/cappuccino,zittix/cappuccino,cappuccino/cappuccino,koamac/Cappuccino,zittix/cappuccino,enquora/cappuccino,deltaprojects/cappuccino,cappuccino/cappuccino,Rosch/cappuccino,Rosch/cappuccino,cacaodev/cappuccino,zittix/cappuccino,tancred/cappuccino,deltaprojects/cappuccino,enquora/cappuccino,primalmotion/cappuccino,FrankReh/cappuccino,Dogild/cappuccino,kidaa/cappuccino,Dogild/cappuccino,rgv151/cappuccino,mrcarlberg/cappuccino,mrcarlberg/cappuccino,deltaprojects/cappuccino,rgv151/cappuccino,mrcarlberg/cappuccino,koamac/Cappuccino,primalmotion/cappuccino,krodelin/cappuccino,cappuccino/cappuccino,Dogild/cappuccino,tancred/cappuccino,wangshijin/cappuccino,tancred/cappuccino,rgv151/cappuccino,zittix/cappuccino,daboe01/cappuccino,rgv151/cappuccino,kidaa/cappuccino,AlexanderMazaletskiy/cappuccino,AlexanderMazaletskiy/cappuccino,daboe01/cappuccino,Dogild/cappuccino,daboe01/cappuccino,kidaa/cappuccino,Rosch/cappuccino,koamac/Cappuccino,wangshijin/cappuccino,cacaodev/cappuccino,deltaprojects/cappuccino,krodelin/cappuccino,enquora/cappuccino,Rosch/cappuccino,daboe01/cappuccino,rgv151/cappuccino,Rosch/cappuccino,primalmotion/cappuccino,daboe01/cappuccino,deltaprojects/cappuccino,cappuccino/cappuccino,krodelin/cappuccino,FrankReh/cappuccino,koamac/Cappuccino,cacaodev/cappuccino,tancred/cappuccino,Dogild/cappuccino,tancred/cappuccino,cacaodev/cappuccino,krodelin/cappuccino,FrankReh/cappuccino,koamac/Cappuccino,kidaa/cappuccino,FrankReh/cappuccino,mrcarlberg/cappuccino,FrankReh/cappuccino,AlexanderMazaletskiy/cappuccino,enquora/cappuccino,cacaodev/cappuccino,AlexanderMazaletskiy/cappuccino,enquora/cappuccino,mrcarlberg/cappuccino,deltaprojects/cappuccino,primalmotion/cappuccino,mrcarlberg/cappuccino,cappuccino/cappuccino,daboe01/cappuccino,kidaa/cappuccino,zittix/cappuccino,cacaodev/cappuccino,daboe01/cappuccino,Dogild/cappuccino,cappuccino/cappuccino,enquora/cappuccino,primalmotion/cappuccino,Rosch/cappuccino,wangshijin/cappuccino,primalmotion/cappuccino,cacaodev/cappuccino,koamac/Cappuccino,zittix/cappuccino,AlexanderMazaletskiy/cappuccino,primalmotion/cappuccino,mrcarlberg/cappuccino,krodelin/cappuccino,Dogild/cappuccino,wangshijin/cappuccino,AlexanderMazaletskiy/cappuccino,deltaprojects/cappuccino,krodelin/cappuccino,kidaa/cappuccino,tancred/cappuccino,mrcarlberg/cappuccino,krodelin/cappuccino,Rosch/cappuccino,wangshijin/cappuccino,cappuccino/cappuccino