CHOP-959: Honor --graphicslevel switch even on first viewer run.

Previous CHOP-959 logic set a flag to remember that settings variable
RenderQualityPerformance was set (by --graphicslevel), so it could be applied
once LLViewerWindow is constructed. But on first viewer run, LLViewerWindow
constructor calls LLFeatureManager::applyRecommendedSettings(), which resets
that settings variable! So don't just set a flag, actually capture the
requested RenderQualityPerformance value for later.