misc/openvdb: fix build with clang 19
Clang 19 now implements CWG 96 [1], which requires a template argument
list after a 'template' keyword, resulting in errors similar to:
/wrkdirs/usr/ports/misc/openvdb/work/openvdb-11.0.0/openvdb/openvdb/../openvdb/tree/NodeManager.h:330:31: error: a template argument list is expected after a name prefixed by the template keyword [-Wmissing-template-arg-list-after-template-kw]
330 | OpT::template eval(mNodeOp, it);
| ^
/wrkdirs/usr/ports/misc/openvdb/work/openvdb-11.0.0/openvdb/openvdb/../openvdb/tree/NodeManager.h:350:31: error: a template argument list is expected after a name prefixed by the template keyword [-Wmissing-template-arg-list-after-template-kw]
350 | OpT::template eval(mNodeOp, it);
| ^
/wrkdirs/usr/ports/misc/openvdb/work/openvdb-11.0.0/openvdb/openvdb/../openvdb/tree/NodeManager.h:375:31: error: a template argument list is expected after a name prefixed by the template keyword [-Wmissing-template-arg-list-after-template-kw]
375 | OpT::template eval(*mNodeOp, it);
| ^In these cases, appending "<>" is enough to satisfy the constraint.
PR: 281418
Approved by: yuri (maintainer)
MFH: 2024Q3
(cherry picked from commit 1f9773e8d9e41c322b14ae6b199bd5a90de27aae)