Minor changes to ALTREP object protection.

Author: tzakharko

src/s2-constructors-formatters.cpp

@@ -112,16 +112,18 @@ SEXP builder_vector_end(const wk_vector_meta_t* meta, void* handler_data) {
   builder_result_finalize(data);
 
   // make the result into a s2_geography object
-  SEXP result = data->result;
-  if (data->use_altrep) result = PROTECT(make_s2_geography_altrep(result));
+  SEXP result;
+  if (data->use_altrep) {
+    result = PROTECT(make_s2_geography_altrep(data->result));
+  } else {
+    result = PROTECT(data->result);
+  }
 
   SEXP cls = PROTECT(Rf_allocVector(STRSXP, 2));
   SET_STRING_ELT(cls, 0, Rf_mkChar("s2_geography"));
   SET_STRING_ELT(cls, 1, Rf_mkChar("wk_vctr"));
   Rf_setAttrib(result, R_ClassSymbol, cls);
-  UNPROTECT(1);
-
-  if (data->use_altrep) UNPROTECT(1);
+  UNPROTECT(2);
 
   return result;
 }