glretrace: Fix snapshots of ES contexts.
glretrace: Fix snapshots of ES contexts.

glReadPixels requires GL_RGBA+GL_UNSGINED_BYTE.

Not sure how long it was broken.  Need to ensure testsuite covers this.

trtt/apitrace,swq0553/apitrace,trtt/apitrace,joshua5201/apitrace,surround-io/apitrace,schulmar/apitrace,schulmar/apitrace,EoD/apitrace,tuanthng/apitrace,surround-io/apitrace,tuanthng/apitrace,swq0553/apitrace,joshua5201/apitrace,apitrace/apitrace,apitrace/apitrace,surround-io/apitrace,schulmar/apitrace,swq0553/apitrace,trtt/apitrace,joshua5201/apitrace,trtt/apitrace,swq0553/apitrace,EoD/apitrace,tuanthng/apitrace,surround-io/apitrace,apitrace/apitrace,EoD/apitrace,joshua5201/apitrace,EoD/apitrace,apitrace/apitrace,EoD/apitrace,swq0553/apitrace,surround-io/apitrace,schulmar/apitrace,tuanthng/apitrace,tuanthng/apitrace,joshua5201/apitrace,trtt/apitrace,schulmar/apitrace