Fixes #4247: remove unnecessary nullptr checks

Author: hribz

src/lstm/recodebeam.cpp

@@ -899,14 +899,11 @@ void RecodeBeamSearch::ContinueContext(
   bool use_dawgs = IsDawgFromBeamsIndex(index);
   NodeContinuation prev_cont = ContinuationFromBeamsIndex(index);
   for (int p = length - 1; p >= 0; --p, previous = previous->prev) {
-    while (previous != nullptr &&
-           (previous->duplicate || previous->code == null_char_)) {
+    while (previous->duplicate || previous->code == null_char_) {
       previous = previous->prev;
     }
-    if (previous != nullptr) {
-      prefix.Set(p, previous->code);
-      full_code.Set(p, previous->code);
-    }
+    prefix.Set(p, previous->code);
+    full_code.Set(p, previous->code);
   }
   if (prev != nullptr && !is_simple_text_) {
     if (top_n_flags_[prev->code] == top_n_flag) {