Signal generator crash fix (#278)

scenes/signal_gen_scene_pwm.c

@@ -53,7 +53,8 @@ bool signal_gen_scene_pwm_on_event(void* context, SceneManagerEvent event) {
         } else if(event.event == SignalGenPwmEventChannelChange) {
             consumed = true;
             // Stop previous channel PWM
-            if(furi_hal_pwm_is_running(app->pwm_ch_prev)) {
+            if(app->pwm_ch_prev != FuriHalPwmOutputIdNone &&
+               furi_hal_pwm_is_running(app->pwm_ch_prev)) {
                 furi_hal_pwm_stop(app->pwm_ch_prev);
             }
 

views/signal_gen_pwm.c

@@ -35,8 +35,8 @@ typedef struct {
 #define VALUE_X 100
 #define VALUE_W 45
 
-#define FREQ_VALUE_X 62
-#define FREQ_MAX 1000000UL
+#define FREQ_VALUE_X   62
+#define FREQ_MAX       1000000UL
 #define FREQ_DIGITS_NB 7
 
 static void pwm_set_config(SignalGenPwm* pwm) {