refactor: extract helper function for safer numeric locale detection

Refactored the detect_numeric_locale function to initialize settings early and extract common logic into single_byte_from_locale_ptr helper, improving code safety and readability without changing behavior.

Author: mattsu2020

src/uu/sort/src/sort.rs

@@ -1287,39 +1287,42 @@ impl FieldSelector {
 
 #[cfg(unix)]
 fn detect_numeric_locale() -> NumericLocaleSettings {
+    let mut settings = NumericLocaleSettings::default();
     unsafe {
         libc::setlocale(libc::LC_NUMERIC, c"".as_ptr());
-        let mut settings = NumericLocaleSettings::default();
-        let conv = libc::localeconv();
-        if conv.is_null() {
-            return settings;
-        }
-
-        let decimal_ptr = (*conv).decimal_point;
-        if !decimal_ptr.is_null() {
-            let decimal_point = CStr::from_ptr(decimal_ptr).to_bytes();
-            if decimal_point.len() == 1 {
-                settings.decimal_pt = Some(decimal_point[0]);
-            }
-        }
-
-        let thousands_ptr = (*conv).thousands_sep;
-        if !thousands_ptr.is_null() {
-            let thousands_sep = CStr::from_ptr(thousands_ptr).to_bytes();
-            if thousands_sep.len() == 1 {
-                settings.thousands_sep = Some(thousands_sep[0]);
-            }
-        }
-
-        settings
     }
+    let conv = unsafe { libc::localeconv() };
+    if conv.is_null() {
+        return settings;
+    }
+    let (decimal_ptr, thousands_ptr) = unsafe {
+        let conv = &*conv;
+        (conv.decimal_point, conv.thousands_sep)
+    };
+
+    settings.decimal_pt = single_byte_from_locale_ptr(decimal_ptr);
+    settings.thousands_sep = single_byte_from_locale_ptr(thousands_ptr);
+    settings
 }
 
 #[cfg(not(unix))]
 fn detect_numeric_locale() -> NumericLocaleSettings {
     NumericLocaleSettings::default()
 }
 
+#[cfg(unix)]
+fn single_byte_from_locale_ptr(ptr: *const libc::c_char) -> Option<u8> {
+    if ptr.is_null() {
+        return None;
+    }
+    let bytes = unsafe { CStr::from_ptr(ptr).to_bytes() };
+    if bytes.len() == 1 {
+        Some(bytes[0])
+    } else {
+        None
+    }
+}
+
 /// Creates an `Arg` for a sort mode flag.
 fn make_sort_mode_arg(mode: &'static str, short: char, help: String) -> Arg {
     Arg::new(mode)