Fix handling of empty host strings

Author: sfackler

openssl/src/x509/verify.rs

@@ -120,9 +120,11 @@ impl X509VerifyParamRef {
     #[corresponds(X509_VERIFY_PARAM_set1_host)]
     pub fn set_host(&mut self, host: &str) -> Result<(), ErrorStack> {
         unsafe {
+            // len == 0 means "run strlen" :(
+            let raw_host = if host.is_empty() { "\0" } else { host };
             cvt(ffi::X509_VERIFY_PARAM_set1_host(
                 self.as_ptr(),
-                host.as_ptr() as *const _,
+                raw_host.as_ptr() as *const _,
                 host.len(),
             ))
             .map(|_| ())