Pcbnew: fix in board editor crash when try to load a footprint from Add footprint tool if the latest loaded footprint was deleted.

In this case, the history has a cleared link that created the crash when the dialog tried to select this deleted FootprintEnumerate

Fixes: lp:1826794
https://bugs.launchpad.net/kicad/+bug/1826794

pcbnew/load_select_footprint.cpp

@@ -233,8 +233,11 @@ MODULE* PCB_BASE_FRAME::SelectFootprintFromLibTree( LIB_ID aPreselect, bool aAll
 
     if( aPreselect.IsValid() )
         adapter->SetPreselectNode( aPreselect, 0 );
-    else if( !historyInfos.empty() )
-        adapter->SetPreselectNode( historyInfos[0]->GetLibId(), 0 );
+    else if( historyInfos.size() )
+    {
+        if( historyInfos[0] )   // Can be null if the footprint was deleted since the last call
+            adapter->SetPreselectNode( historyInfos[0]->GetLibId(), 0 );
+    }
 
     adapter->AddLibraries();