Interpreter and JIT return different capture counts when a recursion returns the called group #1048

Found while working on #1046. When a recursion returns the called group itself through a capture list, the interpreter and JIT report a different number of captures for the same match:

/(?&r(2))(x)?(?(DEFINE)(?<r>(a)))/
    a

/(?&r(2))(x)?(?(DEFINE)(?<r>(a)))/jit
    a

pcre2test output (main at 9b338eb, CMake Release build, JIT on, macOS arm64):

/(?&r(2))(x)?(?(DEFINE)(?<r>(a)))/
    a
 0: a
 1: <unset>
 2: <unset>

/(?&r(2))(x)?(?(DEFINE)(?<r>(a)))/jit
    a
 0: a

Here r is group 2 and (a) is group 3, so (?&r(2)) returns the called group. Both engines leave groups 1 and 2 unset, but the interpreter returns 3 (two trailing <unset> groups) while JIT returns 1. Returning group 3 instead ((?&r(3))) gives the same output in both (3: a, with 1 and 2 unset). The same output is produced with #1046 applied. It is not clear to me which return count is intended here, or whether group 2 should be set to a by the return.