FIRE-34201 - Crash on TP to Mirror

Multiple different crashes seemingly caused by a long  dead volume pointer.
Matches multiple bug splat ids.
Trigger details: have a mirror present and working. TP away, TP to a few other places. Importantly, the other places should not have any mirrors.
TP back to mirror. I believe that because the probe was never overwritten by another, upon return the code tries to reuse it only to find that the pointer is garbage.
The fix tries to ensure that the associated refelction map is cleaned up when the probe goes out of scope.

indra/newview/llheroprobemanager.cpp

@@ -221,6 +221,7 @@ void LLHeroProbeManager::update()
         else
         {
             mNearestHero = nullptr;
+            mDefaultProbe->mViewerObject = nullptr;
         }
 
         mHeroProbeStrength = 1;
@@ -229,6 +230,7 @@ void LLHeroProbeManager::update()
     else
     {
         mNearestHero = nullptr;
+        mDefaultProbe->mViewerObject = nullptr;
     }
     // </FS:Beq>
 }