Bug fix in the LEFT JOIN strength reduction optimization of

check-in [dd568c27b1d76563].  The sqlite3ExprImpliesNotNull() routine was
mistakenly assuming that a CASE expression must always be NULL if contained
any reference to a variable that was NULL.

FossilOrigin-Name: cf171abe954a5f25262161dd69f2e8cecdbf9446c3f6b298201507dbc743567e

src/expr.c

@@ -5012,6 +5012,7 @@ static int impliesNotNullRow(Walker *pWalker, Expr *pExpr){
     case TK_ISNULL:
     case TK_IS:
     case TK_OR:
+    case TK_CASE:
     case TK_FUNCTION:
     case TK_AGG_FUNCTION:
       return WRC_Prune;