RC_Channel: simplify channel check in get_pwm()

libraries/RC_Channel/RC_Channels.cpp

@@ -208,10 +208,10 @@ void RC_Channels::read_mode_switch()
 */
 bool RC_Channels::get_pwm(uint8_t c, uint16_t &pwm) const
 {
-    if (c < 1 || c > NUM_RC_CHANNELS) {
+    RC_Channel *chan = rc_channel(c-1);
+    if (chan == nullptr) {
         return false;
     }
-    RC_Channel *chan = rc_channel(c-1);
     int16_t pwm_signed = chan->get_radio_in();
     if (pwm_signed < 0) {
         return false;

libraries/RC_Channel/examples/RC_Channel/RC_Channel.cpp

@@ -29,7 +29,7 @@ public:
     RC_Channel_Example obj_channels[NUM_RC_CHANNELS];
 
     RC_Channel_Example *channel(const uint8_t chan) override {
-        if (chan > NUM_RC_CHANNELS) {
+        if (chan >= NUM_RC_CHANNELS) {
             return nullptr;
         }
         return &obj_channels[chan];