mol-plugin: fix plugin crash when WebGL is not available

src/apps/basic-wrapper/index.ts

src/apps/demos/lighting/index.ts

src/examples/proteopedia-wrapper/index.ts

src/mol-plugin/behavior/dynamic/labels.ts

...-plugin/behavior/dynamic/volume-streaming/transformers.ts

src/mol-plugin/behavior/static/camera.ts

src/mol-plugin/behavior/static/misc.ts

src/mol-plugin/behavior/static/representation.ts

src/mol-plugin/context.ts

src/mol-plugin/skin/base/components/misc.scss

src/mol-plugin/state.ts

src/mol-plugin/state/transforms/representation.ts

src/mol-plugin/ui/controls/parameters.tsx

src/mol-plugin/ui/image.tsx

src/mol-plugin/ui/structure/selection.tsx

src/mol-plugin/ui/viewport.tsx

src/mol-plugin/util/viewport-screenshot.ts