Check before deferencing, and initialize to NULL.

starseeker · starseeker · commit 345bcd8174bb · 2021-08-16T14:20:57.000-04:00
Crash was observed in Release build for BRL-CAD's step-g on Ubuntu
Linux without this check.
diff --git a/src/clstepcore/complexSupport.h b/src/clstepcore/complexSupport.h
@@ -173,26 +173,27 @@ class SC_CORE_EXPORT EntList {
         // but all we need.
         EntList * firstNot( JoinType );
         EntList * nextNot( JoinType j ) {
-            return next->firstNot( j );
+            return ( next ) ? next->firstNot( j ) : NULL;
         }
         EntList * firstWanted( MatchType );
         EntList * nextWanted( MatchType mat ) {
-            return next->firstWanted( mat );
+            return ( next ) ? next->firstWanted( mat ) : NULL;
         }
         EntList * lastNot( JoinType );
         EntList * prevNot( JoinType j ) {
-            return prev->lastNot( j );
+            return ( prev ) ? prev->lastNot( j ) : NULL;
         }
         EntList * lastWanted( MatchType );
         EntList * prevWanted( MatchType mat ) {
-            return prev->lastWanted( mat );
+            return ( prev ) ? prev->lastWanted( mat ) : NULL;
         }
 
         JoinType join;
         int multiple() {
             return ( join != SIMPLE );
         }
-        EntList * next, *prev;
+        EntList * next = NULL;
+        EntList * prev = NULL;
 
     protected:
         MatchType viable;
