fix(ls): When a file doesn't exist, exit early and fails ls

Currently, running
$ ls doesntexist
will return 0
while it should return 1

Ditto for
$ ls doesntexist a

src/uu/ls/src/ls.rs

@@ -168,11 +168,10 @@ pub fn uumain(args: impl uucore::Args) -> i32 {
         )
         .parse(args);
 
-    list(matches);
-    0
+    list(matches)
 }
 
-fn list(options: getopts::Matches) {
+fn list(options: getopts::Matches) -> i32 {
     let locs: Vec<String> = if options.free.is_empty() {
         vec![String::from(".")]
     } else {
@@ -181,8 +180,16 @@ fn list(options: getopts::Matches) {
 
     let mut files = Vec::<PathBuf>::new();
     let mut dirs = Vec::<PathBuf>::new();
+    let mut has_failed = false;
     for loc in locs {
         let p = PathBuf::from(&loc);
+        if !p.exists() {
+            show_error!("'{}': {}", &loc, "No such file or directory");
+            // We found an error, the return code of ls should not be 0
+            // And no need to continue the execution
+            has_failed = true;
+            continue;
+        }
         let mut dir = false;
 
         if p.is_dir() && !options.opt_present("d") {
@@ -211,6 +218,11 @@ fn list(options: getopts::Matches) {
         }
         enter_directory(&dir, &options);
     }
+    if has_failed {
+        1
+    } else {
+        0
+    }
 }
 
 #[cfg(any(unix, target_os = "redox"))]