readded const

Author: badasahog

src/fread.c

@@ -2544,7 +2544,7 @@ int freadMain(freadMainArgs _args)
             if (thisType != joldType) {             // rare out-of-sample type exception.
               if (!checkedNumberOfFields && !fill) {
                 // check this line has the correct number of fields. If not, don't apply the bump from this invalid line. Instead fall through to myStopEarly below.
-                  char* fieldsRemaining = fieldStart;
+                  const char* fieldsRemaining = fieldStart;
                 if (j + countfields(&fieldsRemaining) != ncol) break;
                 checkedNumberOfFields = true;
               }