Fixed button generation for case when tocref has an unmatched toclabel
Fixed button generation for case when tocref has an unmatched toclabel

mitocw/latex2edx,evheubel/latex2edx,mitocw/latex2edx,evheubel/latex2edx,evheubel/latex2edx,jefrench/latex2edx,jefrench/latex2edx,jefrench/latex2edx,mitocw/latex2edx