fix: empty repo path

e.g. when resolving the string "helix" and interpreting it as a URL because no matching local repo has been found

src/root.rs

@@ -1,4 +1,4 @@
-use anyhow::{Context, Result};
+use anyhow::{Context, Result, anyhow};
 use std::{
     ffi::{OsStr, OsString},
     fs::create_dir_all,
@@ -40,6 +40,9 @@ impl SrcRoot {
     }
 
     fn ensure_repo_checkout(&self, url: &Url) -> Result<PathBuf> {
+        if url.path().is_empty() {
+            return Err(anyhow!("Empty repo path"));
+        }
         let repo_path = self.as_repo_path(url);
         if !repo_path.is_dir() {
             create_dir_all(&repo_path)?;