Fix #14886 fuzzing crash (null-pointer-use) in SymbolDatabase::createSymbolDatabaseIncompleteVars() (cppcheck-opensource#8685)

Author: chrchr-github

lib/symboldatabase.cpp

@@ -1491,7 +1491,7 @@ void SymbolDatabase::createSymbolDatabaseEnums()
 
 void SymbolDatabase::createSymbolDatabaseIncompleteVars()
 {
-    for (Token* tok = mTokenizer.list.front(); tok != mTokenizer.list.back(); tok = tok->next()) {
+    for (Token* tok = mTokenizer.list.front(); precedes(tok, mTokenizer.list.back()); tok = tok->next()) {
         const Scope * scope = tok->scope();
         if (!scope)
             continue;

test/cli/fuzz-crash/crash-60d6b7bc43d21f6a8ad8eb8cca551e45c31c6a32

@@ -0,0 +1 @@
+t
i(){using S};