token_withdraw: avoid silencing errors with is_ok() (#936)

programs/mango-v4/src/health/cache.rs

@@ -820,6 +820,12 @@ impl HealthCache {
             })
     }
 
+    pub fn has_token_info(&self, token_index: TokenIndex) -> bool {
+        self.token_infos
+            .iter()
+            .any(|t| t.token_index == token_index)
+    }
+
     pub fn perp_info(&self, perp_market_index: PerpMarketIndex) -> Result<&PerpInfo> {
         Ok(&self.perp_infos[self.perp_info_index(perp_market_index)?])
     }

programs/mango-v4/src/instructions/token_withdraw.rs

@@ -156,7 +156,7 @@ pub fn token_withdraw(ctx: Context<TokenWithdraw>, amount: u64, allow_borrow: bo
     // Health check
     //
     if let Some((mut health_cache, pre_init_health_lower_bound)) = pre_health_opt {
-        if health_cache.token_info_index(token_index).is_ok() {
+        if health_cache.has_token_info(token_index) {
             // This is the normal case: the health cache knows about the token, we can
             // compute the health for the new state by adjusting its balance
             health_cache.adjust_token_balance(&bank, native_position_after - native_position)?;