mdbx: fix wrong } oops-like typo.

This is a `devel`-only 3-days old regression since a4a35ce9cb.

src/core.c

@@ -5999,6 +5999,7 @@ static txnid_t find_oldest_reader(MDBX_env *env) {
           break;
       }
     }
+  }
 
   if (new_oldest != prev_oldest) {
     mdbx_verbose("update oldest %" PRIaTXN " -> %" PRIaTXN, prev_oldest,
@@ -6006,7 +6007,6 @@ static txnid_t find_oldest_reader(MDBX_env *env) {
     mdbx_assert(env, new_oldest >= lck->mti_oldest_reader.weak);
     atomic_store64(&lck->mti_oldest_reader, new_oldest, mo_Relaxed);
   }
-  }
   return new_oldest;
 }