Handle errors when writing to stdin

When hooks are called, there is an option to feed stdin with a custom
string. However, if any error happen, the .unwrap() causes the daemon
to panic. This fix transforms it into an error than can be handled.

acmed/src/acmed.rs

@@ -138,8 +138,8 @@ impl HookData {
             .spawn()?;
         if hook.stdin.is_some() {
             let data_in = reg.render_template(&hook.stdin.to_owned().unwrap(), &self)?;
-            let stdin = cmd.stdin.as_mut().unwrap();
-            stdin.write_all(data_in.as_bytes()).unwrap();
+            let stdin = cmd.stdin.as_mut().ok_or("stdin not found")?;
+            stdin.write_all(data_in.as_bytes())?;
         }
         Ok(())
     }

acmed/src/errors.rs

@@ -24,6 +24,12 @@ impl From<std::io::Error> for Error {
     }
 }
 
+impl From<&str> for Error {
+    fn from(error: &str) -> Self {
+        Error::new(error)
+    }
+}
+
 impl From<toml::de::Error> for Error {
     fn from(error: toml::de::Error) -> Self {
         Error::new(&format!("IO error: {}", error))