Fixed threads == 0 causing single threaded extraction.

Set exclusive file creation

src/archive.zig

@@ -74,7 +74,7 @@ pub fn initAdvanced(alloc: std.mem.Allocator, fil: File, offset: u64, threads: u
         .parent_alloc = alloc,
         .alloc = .{ .child_allocator = alloc },
         // .fixed_buf = fixed_buf,
-        .thread_count = threads,
+        .thread_count = if (threads > 0) threads else try std.Thread.getCpuCount(),
         .fil = .init(fil, offset),
         .decomp = switch (super.compression) {
             .gzip => Decomp.gzipDecompress,

src/bin/unsquashfs.zig

@@ -15,7 +15,7 @@ const help_mgs =
     \\
     \\  -o <offset>     Start reading the archive at the given offset.
     \\
-    \\  -p <threads>    Specify how many threads to use. If no present, the system's logical cores count is used.
+    \\  -p <threads>    Specify how many threads to use. If no present or zero, the system's logical cores count is used.
     \\
     \\  --help          Display this messages
     \\  --version       Display the version
@@ -83,9 +83,9 @@ fn handleArgs(alloc: std.mem.Allocator, out: *Writer) !void {
             };
             continue;
         } else if (std.mem.eql(u8, arg, "--version")) {
-            try out.print("zig-unsquashfs version ", .{});
+            try out.print("zig-unsquashfs v", .{});
             try config.version.format(out);
-            try out.print("\nBuilt using Zig {s} with {} backend in {} mode.\n", .{ builtin.zig_version_string, builtin.zig_backend, builtin.mode });
+            try out.print("\nBuilt using Zig {s}\n", .{ builtin.zig_version_string, builtin.zig_backend, builtin.mode });
             std.process.exit(0);
             return;
         } else if (std.mem.eql(u8, arg, "--help")) {