ZJIT: Fix assertion failure when profiling VM_BLOCK_HANDLER_NONE

As can be seen in vm_block_handler_verify(), VM_BLOCK_HANDLER_NONE is
not a valid argument for vm_block_handler(). Store nil in the profiler
when seen instead of crashing.

vm_insnhelper.c

@@ -6041,11 +6041,14 @@ vm_define_method(const rb_execution_context_t *ec, VALUE obj, ID id, VALUE iseqv
 }
 
 // Return the untagged block handler:
+// * If it's VM_BLOCK_HANDLER_NONE, return nil
 // * If it's an ISEQ or an IFUNC, fetch it from its rb_captured_block
 // * If it's a PROC or SYMBOL, return it as is
 static VALUE
 rb_vm_untag_block_handler(VALUE block_handler)
 {
+    if (VM_BLOCK_HANDLER_NONE == block_handler) return Qnil;
+
     switch (vm_block_handler_type(block_handler)) {
       case block_handler_type_iseq:
       case block_handler_type_ifunc: {

zjit/src/profile.rs

@@ -361,3 +361,17 @@ impl IseqProfile {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::cruby::*;
+
+    #[test]
+    fn can_profile_block_handler() {
+        with_rubyvm(|| eval("
+            def foo = yield
+            foo rescue 0
+            foo rescue 0
+        "));
+    }
+}