Make sure inputFlatNoNulls_ is initialized in ctor (facebookincubator…

…#11140)

Summary:
Pull Request resolved: facebookincubator#11140

when `inputFlatNoNulls_` is not initialized, it could result in undefined behavior like one described in https://www.internalfb.com/diff/D63556283?dst_version_fbid=804905691596581&transaction_fbid=550949777494622

This diff initializes inputFlatNoNulls_ as false.

Differential Revision: D63673714

velox/expression/EvalCtx.cpp

@@ -46,6 +46,7 @@ EvalCtx::EvalCtx(core::ExecCtx* execCtx, ExprSet* exprSet, const RowVector* row)
 EvalCtx::EvalCtx(core::ExecCtx* execCtx)
     : execCtx_(execCtx), exprSet_(nullptr), row_(nullptr) {
   VELOX_CHECK_NOT_NULL(execCtx);
+  inputFlatNoNulls_ = false;
 }
 
 void EvalCtx::saveAndReset(ContextSaver& saver, const SelectivityVector& rows) {