Update positive method in Checks class to allow zero as a valid input, enhancing validation logic for user input.

shop/checks.py

@@ -32,7 +32,7 @@ class Checks:
             return False
 
     def positive(self, m):
-        return self.same(m) and m.content.isdigit() and int(m.content) > 0
+        return self.same(m) and m.content.isdigit() and int(m.content) >= 0
 
     def role(self, m):
         roles = [r.name for r in self.ctx.guild.roles if r.name != "Bot"]