Exec command directly if subshell fails

If execing the child fails, it might be because the shell doesn't exist.
Try running the command directly before giving up.

src/main.zig

···
                     .stdout = .pipe,
                     .stderr = .ignore,
                     .stdin = .ignore,
-                }) catch continue;
+                }) catch |err| switch (err) {
+                    error.AccessDenied,
+                    error.FileBusy,
+                    error.FileNotFound,
+                    error.FileSystem,
+                    error.InvalidExe,
+                    error.IsDir,
+                    error.NotDir,
+                    error.OutOfMemory,
+                    error.PermissionDenied,
+                    error.SymLinkLoop,
+                    error.SystemResources,
+                    => blk: {
+                        var argv_buf: [128][]const u8 = undefined;
+                        var argv: ArrayList([]const u8) = .initBuffer(&argv_buf);
+                        var payload_iter = std.mem.splitAny(u8, connection_payload, " \t\n");
+                        while (payload_iter.next()) |arg| argv.appendBounded(arg) catch continue;
+                        break :blk std.process.spawn(init.io, .{
+                            .argv = argv.items,
+                            .stdout = .pipe,
+                            .stderr = .ignore,
+                            .stdin = .ignore,
+                        }) catch continue;
+                    },
+                    error.Canceled,
+                    error.NoDevice,
+                    error.OperationUnsupported,
+                    => |e| return e,
+                    else => continue,
+                };
 
                 var child_output_buf: [SaprusClient.max_payload_len]u8 = undefined;
                 var child_output_reader = child.stdout.?.reader(init.io, &child_output_buf);