fix inverted logic

Author: danieleades

src/cargo/core/features.rs

@@ -841,13 +841,13 @@ impl CliUnstable {
                 // some point, and migrate to a new -Z flag for any future
                 // things.
                 let feats = parse_features(v);
-                let stab_is_empty = feats.iter().any(|feat| {
+                let stab_is_not_empty = feats.iter().any(|feat| {
                     matches!(
                         feat.as_str(),
                         "build_dep" | "host_dep" | "dev_dep" | "itarget" | "all"
                     )
                 });
-                if !stab_is_empty || feats.is_empty() {
+                if stab_is_not_empty || feats.is_empty() {
                     // Make this stabilized_err once -Zfeature support is removed.
                     stabilized_warn(k, "1.51", STABILIZED_FEATURES);
                 }