Allow freezing temperatures

But not on Ultimaker printers, because they crash.

resources/definitions/fdmprinter.def.json

@@ -1053,7 +1053,7 @@
                     "unit": "°C",
                     "type": "float",
                     "default_value": 210,
-                    "minimum_value": "0",
+                    "minimum_value": "-273.15",
                     "maximum_value_warning": "260",
                     "enabled": "not (material_flow_dependent_temperature)",
                     "settable_per_mesh": false,
@@ -1090,7 +1090,7 @@
                     "unit": "°C",
                     "type": "float",
                     "default_value": 60,
-                    "minimum_value": "0",
+                    "minimum_value": "-273.15",
                     "maximum_value_warning": "260",
                     "enabled": "machine_heated_bed",
                     "settable_per_mesh": false,
@@ -1269,7 +1269,7 @@
                     "type": "float",
                     "unit": "°C",
                     "default_value": 150,
-                    "minimum_value": "0",
+                    "minimum_value": "-273.15",
                     "maximum_value_warning": "260",
                     "settable_per_mesh": false,
                     "settable_per_extruder": true

resources/definitions/ultimaker.def.json

@@ -7,5 +7,16 @@
         "author": "Ultimaker",
         "manufacturer": "Ultimaker",
         "visible": false
+    },
+    "overrides": {
+        "material_print_temperature": {
+            "minimum_value": "0"
+        },
+        "material_bed_temperature": {
+            "minimum_value": "0"
+        },
+        "material_standby_temperature": {
+            "minimum_value": "0"
+        }
     }
 }