Fix heap-use-after-free in VlRNG::VlRNG() (#7865)

docs/CONTRIBUTORS

@@ -61,6 +61,7 @@ David Turner
 Dercury
 Diego Roux
 Dominick Grochowina
+Dragon-Git
 Don Williamson
 Drew Ranck
 Drew Taussig

include/verilated_types.h

@@ -337,6 +337,7 @@ public:
 
     ~VlProcess() {
         if (m_parentp) m_parentp->detach(this);
+        if (t_currentp == this) t_currentp = m_parentp.get();
     }
 
     void attach(VlProcess* childp) { m_children.insert(childp); }