src: refactor SSLError case statement

- Don't use both break and return simultaneously.
- Use case:/UNREACHABLE() to enforce that all cases are handled, instead
  of CHECK().

Backport-PR-URL: #25968
PR-URL: #25861
Reviewed-By: Fedor Indutny <fedor.indutny@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>

src/tls_wrap.cc

@@ -347,14 +347,15 @@ Local<Value> TLSWrap::GetSSLError(int status, int* err, std::string* msg) {
     case SSL_ERROR_WANT_READ:
     case SSL_ERROR_WANT_WRITE:
     case SSL_ERROR_WANT_X509_LOOKUP:
-      break;
+      return Local<Value>();
+
     case SSL_ERROR_ZERO_RETURN:
       return scope.Escape(env()->zero_return_string());
-      break;
-    default:
-      {
-        CHECK(*err == SSL_ERROR_SSL || *err == SSL_ERROR_SYSCALL);
 
+    case SSL_ERROR_SSL:
+    case SSL_ERROR_SYSCALL:
+      {
+        unsigned long ssl_err = ERR_peek_error();  // NOLINT(runtime/int)
         BIO* bio = BIO_new(BIO_s_mem());
         ERR_print_errors(bio);
 
@@ -372,8 +373,11 @@ Local<Value> TLSWrap::GetSSLError(int status, int* err, std::string* msg) {
 
         return scope.Escape(exception);
       }
+
+    default:
+      UNREACHABLE();
   }
-  return Local<Value>();
+  UNREACHABLE();
 }