Fixed: When selector is only a ':' in a send message statement the new compiler crashed.

The program below crashed on the last line with a 'null is not an object' error message. Also added a test case.

@implementation MyObject {
- (int):(int)a {
  return a;
}
@end
var a = [[MyObject alloc] init];
var b = [a:3];
Merge pull request #1937 from mrcarlberg/colon_selector

Fixed: When selector is only a ':' in a send message statement the new compiler crashed.