Throw bed min temp error only if heating

Marlin/temperature.cpp

@@ -1822,8 +1822,8 @@ void Temperature::isr() {
       #else
         #define GEBED >=
       #endif
-      if (current_temperature_bed_raw GEBED bed_maxttemp_raw) _temp_error(-1, PSTR(MSG_T_MAXTEMP), PSTR(MSG_ERR_MAXTEMP_BED));
-      if (bed_minttemp_raw GEBED current_temperature_bed_raw) _temp_error(-1, PSTR(MSG_T_MINTEMP), PSTR(MSG_ERR_MINTEMP_BED));
+      if (current_temperature_bed_raw GEBED bed_maxttemp_raw) max_temp_error(-1);
+      if (bed_minttemp_raw GEBED current_temperature_bed_raw && target_temperature_bed > 0.0f) min_temp_error(-1);
     #endif
 
   } // temp_count >= OVERSAMPLENR