[master] fd7c8bfca assert that esi requests do start on vcl0

[Nils Goroll]

commit fd7c8bfca2c0ca7a00477618d80c2aab34b84903
Author: Nils Goroll <nils.goroll at uplex.de>
Date:   Wed Nov 13 12:00:37 2019 +0100

    assert that esi requests do start on vcl0
    
    ... which is the vcl the topreq started on

diff --git a/bin/varnishd/cache/cache_vpi.c b/bin/varnishd/cache/cache_vpi.c
index 565536f74..8a345ba41 100644
--- a/bin/varnishd/cache/cache_vpi.c
+++ b/bin/varnishd/cache/cache_vpi.c
@@ -96,6 +96,9 @@ VPI_vcl_select(VRT_CTX, VCL_VCL vcl)
 	if ((IS_TOPREQ(req) && req->top->vcl0 != NULL) || req->restarts > 0)
 		return;		// Illegal, req-FSM will fail this later.
 
+	if (! IS_TOPREQ(req))
+		assert(req->vcl == req->top->vcl0);
+
 	/* XXX VCL_Task* are somewhat duplicated to those in Req_Rollback called
 	 * from FSM for VCL_RET_VCL. Keeping them here to ensure there are no
 	 * tasks during calls to VCL_Rel / vcl_get