-disable TEMP Min MAX Kill while using PS_ON Pin

ON GEN7 there is no temperature reading when power is off.. so Marlin
would kill itself. There seems to be an update from "Traumflug" on GEN7
using standby VCC for thermistors.

Marlin/temperature.cpp

@@ -763,13 +763,21 @@ ISR(TIMER0_COMPB_vect)
     for(unsigned char e = 0; e < EXTRUDERS; e++) {
        if(current_raw[e] >= maxttemp[e]) {
           target_raw[e] = 0;
-          max_temp_error(e);
-          kill();;
+          #if (PS_ON != -1)
+          {
+            max_temp_error(e);
+            kill();;
+          }
+          #endif
        }
        if(current_raw[e] <= minttemp[e]) {
           target_raw[e] = 0;
-          min_temp_error(e);
-          kill();
+          #if (PS_ON != -1)
+          {
+            min_temp_error(e);
+            kill();
+          }
+          #endif
        }
     }