[PATCH proxmox] rest-server: throw meaningful error if template file does not exist

[Christoph Heiss <c.heiss@proxmox.com>]

Otherwise, users just fail on startup while constructing an `ApiConfig`
instance, with this pretty unhelpful error message:

  Error: No such file or directory (os error 2)

Give some context to make it easier to trace down these errors in the
future.

Signed-off-by: Christoph Heiss <c.heiss@proxmox.com>
---
Noticed this while building the latest master of
proxmox-datacenter-manager, which requires a new template as of

  60a1c406 ("server: add and serve template for novnc")

.. but the corresponding package hasn't been bumped yet.

 proxmox-rest-server/src/api_config.rs | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/proxmox-rest-server/src/api_config.rs b/proxmox-rest-server/src/api_config.rs
index 6c5c0aea..2f590018 100644
--- a/proxmox-rest-server/src/api_config.rs
+++ b/proxmox-rest-server/src/api_config.rs
@@ -421,6 +421,10 @@ mod templates {
             }
 
             let path: PathBuf = path.into();
+            if !path.exists() {
+                bail!("template file not found: {}", path.display());
+            }
+
             let metadata = metadata(&path)?;
             let mtime = metadata.modified()?;
 
-- 
2.54.0