fix: don't panic if the handshake wasn't performed - instead return an error.

This makes the system more reliable, particularly when certain operations are
performed on Drop, and can happen prematurely.

Author: Byron

Diff for: gix-transport/src/client/blocking_io/file.rs

@@ -109,7 +109,7 @@ impl client::TransportWithoutIO for SpawnProcessOnDemand {
     ) -> Result<RequestWriter<'_>, client::Error> {
         self.connection
             .as_mut()
-            .expect("handshake() to have been called first")
+            .ok_or(client::Error::MissingHandshake)?
             .request(write_mode, on_into_read, trace)
     }
 

Diff for: gix-transport/src/client/blocking_io/http/mod.rs

@@ -333,7 +333,7 @@ impl<H: Http> client::TransportWithoutIO for Transport<H> {
         on_into_read: MessageKind,
         trace: bool,
     ) -> Result<RequestWriter<'_>, client::Error> {
-        let service = self.service.expect("handshake() must have been called first");
+        let service = self.service.ok_or(client::Error::MissingHandshake)?;
         let url = append_url(&self.url, service.as_str());
         let static_headers = &[
             Cow::Borrowed(self.user_agent_header),

Diff for: gix-transport/src/client/non_io_types.rs

@@ -112,6 +112,8 @@ mod error {
     #[derive(thiserror::Error, Debug)]
     #[allow(missing_docs)]
     pub enum Error {
+        #[error("A request was performed without performing the handshake first")]
+        MissingHandshake,
         #[error("An IO error occurred when talking to the server")]
         Io(#[from] std::io::Error),
         #[error("Capabilities could not be parsed")]