Check that there is a package for 'sdist create'

src/dds/cli/cmd/sdist_create.cpp

 #include "../options.hpp"
 
+#include <dds/error/errors.hpp>
 #include <dds/sdist/dist.hpp>
 
 #include <fmt/core.h>
         .include_apps  = true,
         .include_tests = true,
     };
-    auto pkg_man          = package_manifest::load_from_directory(params.project_dir);
+    auto pkg_man = package_manifest::load_from_directory(params.project_dir);
+    if (!pkg_man) {
+        dds::throw_user_error<
+            errc::invalid_pkg_filesystem>("The source root at [{}] is not a valid dds source root",
+                                          params.project_dir.string());
+    }
     auto default_filename = fmt::format("{}.tar.gz", pkg_man->id.to_string());
     auto filepath         = opts.out_path.value_or(fs::current_path() / default_filename);
     create_sdist_targz(filepath, params);