C++: Do not consider expression results discardable when there is a conversion

Author: jketema

cpp/ql/lib/semmle/code/cpp/ir/implementation/raw/internal/TranslatedExpr.qll

@@ -4146,7 +4146,8 @@ predicate exprNeedsCopyIfNotLoaded(Expr expr) {
 private predicate exprImmediatelyDiscarded(Expr expr) {
   exists(ExprStmt s |
     s = expr.getParent() and
-    not exists(StmtExpr se | s = se.getStmt().(BlockStmt).getLastStmt())
+    not exists(StmtExpr se | s = se.getStmt().(BlockStmt).getLastStmt()) and
+    not exists(Conversion c | c = expr.getConversion*() and not isTransparentConversion(c))
   )
   or
   exists(CommaExpr c | c.getLeftOperand() = expr)