[Joints] Fix warning.

I don't know why, but for some old compiler, they cannot guess right template arguments.
Should be fixed later.
12 jobs for v1.2.6 in 11 seconds (queued for 3 seconds)
latest
Status Name Job ID Coverage
  Minimal
failed build_minimal_14 #3768

00:00:03

failed build_minimal_16 #3767

00:00:04

failed build_minimal_zesty #3769
allowed to fail

00:00:04

failed build_minimal_14 #3728

00:00:04

failed build_minimal_14 #3758

00:00:06

failed build_minimal_16 #3729

00:00:03

failed build_minimal_16 #3759

00:00:06

failed build_minimal_zesty #3730
allowed to fail

00:00:04

failed build_minimal_zesty #3760
allowed to fail

00:00:07

 
  Full
skipped build_full_14 #3731
skipped build_full_16 #3732
skipped build_full_zesty #3733
allowed to fail
 
Name Stage Failure
failed
build_minimal_zesty Minimal
No job log
failed
build_minimal_14 Minimal
No job log
failed
build_minimal_16 Minimal
No job log