Refine type of SmtpState.doing_jobs to bool

src/context.rs

@@ -107,7 +107,7 @@ impl Default for BobStatus {
 pub struct SmtpState {
     pub idle: bool,
     pub suspended: bool,
-    pub doing_jobs: i32,
+    pub doing_jobs: bool,
     pub perform_jobs_needed: i32,
     pub probe_network: bool,
 }