fix min and max setter for ui.number (fixes #2950)

nicegui/elements/number.py

@@ -72,7 +72,7 @@ class Number(ValidationElement, DisableableElement):
 
     @min.setter
     def min(self, value: float) -> None:
-        if self._props['min'] == value:
+        if self._props.get('min') == value:
             return
         self._props['min'] = value
         self.sanitize()
@@ -85,7 +85,7 @@ class Number(ValidationElement, DisableableElement):
 
     @max.setter
     def max(self, value: float) -> None:
-        if self._props['max'] == value:
+        if self._props.get('max') == value:
             return
         self._props['max'] = value
         self.sanitize()