Bug 1751008 - Ensure we mark GLFeature::transform_feedback2 as unsupported if symbol load fails. r=jgilbert

When loading the symbols for transform_feedback2, we marked it as for
texture_storage. This would mean that if draw_buffers_indexed loading
failed, and we checked for the feature support, it would indicate it is
supported even though it is backed by nothing.

Differential Revision: https://phabricator.services.mozilla.com/D136388

gfx/gl/GLContext.cpp

@@ -1152,7 +1152,7 @@ void GLContext::LoadMoreSymbols(const SymbolLoader& loader) {
             { (PRFuncPtr*) &mSymbols.fResumeTransformFeedback, {{ "glResumeTransformFeedbackNV" }} },
             END_SYMBOLS
         };
-        if (!fnLoadFeatureByCore(coreSymbols, extSymbols, GLFeature::texture_storage)) {
+        if (!fnLoadFeatureByCore(coreSymbols, extSymbols, GLFeature::transform_feedback2)) {
             // Also mark bind_buffer_offset as unsupported.
             MarkUnsupported(GLFeature::bind_buffer_offset);
         }