flamenco: fix custom err default

Author: cali-jumptrading

contrib/test/test-vectors-commit-sha.txt

@@ -1 +1 @@
-40bf836f7e741203f05c9e9b4f11c9aca3cc9a4d
+b80c2beb881bb1dd5c296f7d564849dabc8c32ee

src/flamenco/log_collector/fd_log_collector.h

@@ -465,7 +465,7 @@ fd_log_collector_program_failure( fd_exec_instr_ctx_t * ctx ) {
   char custom_err[33] = { 0 };
   const char * err = custom_err;
   const fd_exec_txn_ctx_t * txn_ctx = ctx->txn_ctx;
-  if( txn_ctx->custom_err != UINT_MAX ) {
+  if( FD_UNLIKELY( txn_ctx->custom_err!=0U ) ) {
     /* Max msg_sz = 32 <= 66 */
     snprintf( custom_err, sizeof(custom_err), "custom program error: 0x%x", txn_ctx->custom_err );
   } else if( txn_ctx->exec_err ) {

src/flamenco/runtime/context/fd_exec_txn_ctx.c

@@ -176,7 +176,7 @@ void
 fd_exec_txn_ctx_setup_basic( fd_exec_txn_ctx_t * ctx ) {
   fd_compute_budget_details_new( &ctx->compute_budget_details );
 
-  ctx->custom_err                = UINT_MAX;
+  ctx->custom_err                = 0U;
   ctx->instr_stack_sz            = 0;
   ctx->accounts_cnt              = 0UL;
   ctx->executable_cnt            = 0UL;