Fix valid range with valid min/max check logic

Fixes a logic error in valid_range with valid_min/valid_max which
resulted in erroneous results.

compliance_checker/cf/cf_1_6.py

@@ -443,15 +443,19 @@ def check_valid_range_or_valid_min_max_present(self, ds):
         total = 0
 
         for variable in ds.variables.values():
-            if hasattr(variable, "valid_max") and (
-                hasattr(variable, "valid_min") or hasattr(variable, "valid_range")
-            ):
-                total = total + 1
-
-                fails.append(
-                    f"For the variable {variable.name} the valid_range attribute must not be present "
-                    "if the valid_min and/or valid_max attributes are present",
-                )
+            if (hasattr(variable, "valid_max") or
+                hasattr(variable, "valid_min")):
+                total += 1
+                # if there's also valid_range in addition to
+                # valid_min/valid_max, this is not compliant
+                if hasattr(variable, "valid_range"):
+                    fails.append(
+                        f"For the variable {variable.name} the valid_range attribute must not be present "
+                        "if the valid_min and/or valid_max attributes are present",
+                    )
+            # *Just* valid_range should be added to total as well
+            elif hasattr(variable, "valid_range"):
+                total += 1
 
         return Result(
             BaseCheck.MEDIUM,