Activate BED_MINTEMP error.

And call _temp_error() directly for ERR_MAXTEMP_BED to avoid the only one time use of bed_max_temp_error().

Includes #2156.

Marlin/language_en.h

 #ifndef MSG_ERR_MAXTEMP_BED
 #define MSG_ERR_MAXTEMP_BED                 "Err: MAXTEMP BED"
 #endif
+#ifndef MSG_ERR_MINTEMP_BED
+#define MSG_ERR_MINTEMP_BED                 "Err: MINTEMP BED"
+#endif
 #ifndef MSG_END_HOUR
 #define MSG_END_HOUR                        "hours"
 #endif

Marlin/temperature.cpp

 static int maxttemp_raw[EXTRUDERS] = ARRAY_BY_EXTRUDERS( HEATER_0_RAW_HI_TEMP , HEATER_1_RAW_HI_TEMP , HEATER_2_RAW_HI_TEMP, HEATER_3_RAW_HI_TEMP);
 static int minttemp[EXTRUDERS] = { 0 };
 static int maxttemp[EXTRUDERS] = ARRAY_BY_EXTRUDERS( 16383, 16383, 16383, 16383 );
-//static int bed_minttemp_raw = HEATER_BED_RAW_LO_TEMP; /* No bed mintemp error implemented?!? */
+#ifdef BED_MINTEMP
+static int bed_minttemp_raw = HEATER_BED_RAW_LO_TEMP;
+#endif
 #ifdef BED_MAXTEMP
   static int bed_maxttemp_raw = HEATER_BED_RAW_HI_TEMP;
 #endif
 void min_temp_error(uint8_t e) {
   _temp_error(e, PSTR(MSG_T_MINTEMP), PSTR(MSG_ERR_MINTEMP));
 }
-void bed_max_temp_error(void) {
-  _temp_error(-1, PSTR(MSG_T_MAXTEMP), PSTR(MSG_ERR_MAXTEMP_BED));
-}
 
 float get_pid_output(int e) {
   float pid_output;
   #endif // EXTRUDERS > 1
 
   #ifdef BED_MINTEMP
-    /* No bed MINTEMP error implemented?!? */ /*
     while(analog2tempBed(bed_minttemp_raw) < BED_MINTEMP) {
       #if HEATER_BED_RAW_LO_TEMP < HEATER_BED_RAW_HI_TEMP
         bed_minttemp_raw += OVERSAMPLENR;
         bed_minttemp_raw -= OVERSAMPLENR;
       #endif
     }
-    */
   #endif //BED_MINTEMP
   #ifdef BED_MAXTEMP
     while(analog2tempBed(bed_maxttemp_raw) > BED_MAXTEMP) {
       #else
         #define GEBED >=
       #endif
-      if (current_temperature_bed_raw GEBED bed_maxttemp_raw) bed_max_temp_error();
+      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));
     #endif
 
   } // temp_count >= OVERSAMPLENR