MaterialPreviewRenderer: fix typo causing renderbuffer to be set to 1 instead of -1 if failure occurs and thus being accidentally deleted.
MaterialPreviewRenderer: fix typo causing renderbuffer to be set to 1 instead of -1 if failure occurs and thus being accidentally deleted.

zhukaixy/open3mod,dayo7116/open3mod,zhukaixy/open3mod,acgessler/open3mod,acgessler/open3mod,dayo7116/open3mod