client: simplify monitor type handling

I think the original logic is correct, but I'm not sure.
Cleverness to avoiding storing a Structure pointer is a
premature optimization anyway.

src/client/monitor.cpp

@@ -155,6 +155,7 @@ void MonitorFIFO::open(const pvd::StructureConstPtr& type)
 
         opened = true;
         needConnected = true;
+        this->type = type;
 
         if(conf.ignoreRequestMask) {
             selectMask.clear();
@@ -187,6 +188,7 @@ void MonitorFIFO::close()
     opened = false;
     needClosed = true;
     selectMask.clear();
+    type.reset();
 }
 
 void MonitorFIFO::finish()
@@ -227,7 +229,7 @@ bool MonitorFIFO::tryPost(const pvData::PVStructure& value,
         empty.pop_front();
     } else if(force) {
         // allocate an extra element
-        elem.reset(new MonitorElement(pvd::getPVDataCreate()->createPVStructure(inuse.back()->pvStructurePtr->getStructure())));
+        elem.reset(new MonitorElement(pvd::getPVDataCreate()->createPVStructure(type)));
     }
 
     if(elem) {

src/client/pv/monitor.h

@@ -388,6 +388,8 @@ private:
     size_t freeHighLevel;
     epicsInt32 flowCount;
 
+    epics::pvData::StructureConstPtr type; // NULL if not opened
+
     typedef std::list<MonitorElementPtr> buffer_t;
     // we allocate one extra buffer element to hold data when post()
     // while all elements poll()'d.  So there will always be one