SOFT_PWM: Do not switch off heaters twice on pwm_count wraparound

After wraparound, pwm_count <= pwm_mask holds, thus soft_pwm_X <= pwm_count
guarantees soft_pwm_X < pwm_mask is true, and the heater will be switched
off in the first branch.
Do not evaluate the pwm conditions a second time, this reduces the
instruction count (4 instructions per PWM) and text size (6 byte).

Signed-off-by: Stefan Brüns <stefan.bruens@rwth-aachen.de>

Marlin/temperature.cpp

@@ -1594,17 +1594,17 @@ void Temperature::isr() {
         #endif
       #endif
     }
-
+    else {
       if (soft_pwm_0 <= pwm_count_tmp) WRITE_HEATER_0(0);
       #if HOTENDS > 1
         if (soft_pwm_1 <= pwm_count_tmp) WRITE_HEATER_1(0);
+      #endif
       #if HOTENDS > 2
         if (soft_pwm_2 <= pwm_count_tmp) WRITE_HEATER_2(0);
+      #endif
       #if HOTENDS > 3
         if (soft_pwm_3 <= pwm_count_tmp) WRITE_HEATER_3(0);
       #endif
-      #endif
-    #endif
 
       #if HAS_HEATER_BED
         if (soft_pwm_BED <= pwm_count_tmp) WRITE_HEATER_BED(0);
@@ -1621,6 +1621,7 @@ void Temperature::isr() {
           if (soft_pwm_fan[2] <= pwm_count_tmp) WRITE_FAN2(0);
         #endif
       #endif
+    }
 
     // SOFT_PWM_SCALE to frequency:
     //