Context Masquerade cannot handle both hash and extension strive from config

[scheibel]

When using both a hash and a extension-strive array in the masquerade config, the line https://github.com/cginternals/webgl-operate/blob/master/source/contextmasquerade.ts#L88 initializes the wanted extensions from the hash and https://github.com/cginternals/webgl-operate/blob/master/source/contextmasquerade.ts#L100 overwrites it without any merge of both information sources.