Fix controllerFan() code

- Add support for 4th extruder
- Fix parentheses matching
- Apply coding standards
- Address issue mentioned at #1575

Marlin/Marlin_main.cpp

   #endif
 #endif
 
-unsigned long lastMotor = 0; //Save the time for when a motor was turned on last
-unsigned long lastMotorCheck = 0;
-
-void controllerFan()
-{
-  if ((millis() - lastMotorCheck) >= 2500) //Not a time critical function, so we only check every 2500ms
-  {
-    lastMotorCheck = millis();
-	
-    if((X_ENABLE_READ) == (X_ENABLE_ON)) || (Y_ENABLE_READ) == (Y_ENABLE_ON)) || (Z_ENABLE_READ) == (Z_ENABLE_ON)) || (soft_pwm_bed > 0)
-    #if EXTRUDERS > 2
-       || (E2_ENABLE_READ) == (E_ENABLE_ON))
-    #endif
-    #if EXTRUDER > 1
-      #if defined(X2_ENABLE_PIN) && X2_ENABLE_PIN > -1
-       || (X2_ENABLE_READ) == (X_ENABLE_ON))
+unsigned long lastMotor = 0; // Last time a motor was turned on
+unsigned long lastMotorCheck = 0; // Last time the state was checked
+
+void controllerFan() {
+  uint32_t ms = millis();
+  if (ms >= lastMotorCheck + 2500) { // Not a time critical function, so we only check every 2500ms
+    lastMotorCheck = ms;
+    if (X_ENABLE_READ == X_ENABLE_ON || Y_ENABLE_READ == Y_ENABLE_ON || Z_ENABLE_READ == Z_ENABLE_ON || soft_pwm_bed > 0
+      || E0_ENABLE_READ == E_ENABLE_ON // If any of the drivers are enabled...
+      #if EXTRUDERS > 1
+        || E1_ENABLE_READ == E_ENABLE_ON
+        #if defined(X2_ENABLE_PIN) && X2_ENABLE_PIN > -1
+          || X2_ENABLE_READ == X_ENABLE_ON
+        #endif
+        #if EXTRUDERS > 2
+          || E2_ENABLE_READ == E_ENABLE_ON
+          #if EXTRUDERS > 3
+            || E3_ENABLE_READ == E_ENABLE_ON
+          #endif
+        #endif
       #endif
-       || (E1_ENABLE_READ) == (E_ENABLE_ON))
-    #endif
-       || (E0_ENABLE_READ) == (E_ENABLE_ON))) //If any of the drivers are enabled...
-    {
-      lastMotor = millis(); //... set time to NOW so the fan will turn on
-    }
-
-    if ((millis() - lastMotor) >= (CONTROLLERFAN_SECS*1000UL) || lastMotor == 0) //If the last time any driver was enabled, is longer since than CONTROLLERSEC...
-    {
-        digitalWrite(CONTROLLERFAN_PIN, 0);
-        analogWrite(CONTROLLERFAN_PIN, 0);
-    }
-    else
-    {
-        // allows digital or PWM fan output to be used (see M42 handling)
-        digitalWrite(CONTROLLERFAN_PIN, CONTROLLERFAN_SPEED);
-        analogWrite(CONTROLLERFAN_PIN, CONTROLLERFAN_SPEED);
+    ) {
+      lastMotor = ms; //... set time to NOW so the fan will turn on
     }
+    uint8_t speed = (lastMotor == 0 || ms >= lastMotor + (CONTROLLERFAN_SECS * 1000UL)) ? 0 : CONTROLLERFAN_SPEED;
+    // allows digital or PWM fan output to be used (see M42 handling)
+    digitalWrite(CONTROLLERFAN_PIN, speed);
+    analogWrite(CONTROLLERFAN_PIN, speed);
   }
 }
 #endif