Fixes https://debbugs.gnu.org/63279. The issue was that if the producer
thunk caused a backtrace, pretty-printing the call-with-values frame
would segfault because there was an unininitialized slot on the stack.
For functions produced by the compiler this wouldn't be a problem
because there are stack maps, but primitives require that all slots on a
pending stack frame be packed (no uninitialized values) and tagged (all
SCM values, no unboxed values).
* test-suite/tests/error-handling.test: New test.
* test-suite/Makefile.am: Add new file.
* libguile/vm.c (define_vm_builtins): Fix call-with-values to have a
more compact stack.
