Improve handling NULL characters

inst/tests/tests.Rraw

@@ -14008,6 +14008,9 @@ DT = data.table(x=c("a","b","c","b","a","c"), y=c(1,3,6,1,6,3), v=1:6)
 setindex(DT, y)
 test(2024, DT[y==6, v:=10L, verbose=TRUE], output=c("Constructing irows for.*", "Reorder irows for.*"))
 
+# fread embedded NULL, #3400
+test(2025, fread(testDir("issue_3400_fread.txt"), skip=1, header=TRUE), data.table(A=INT(1,3), B=INT(2,2), C=INT(3,1)))
+
 
 ###################################
 #  Add new tests above this line  #

src/fread.c

@@ -2149,7 +2149,10 @@ int freadMain(freadMainArgs _args) {
           while (*tch==' ') tch++;  // multiple sep=' ' at the tLineStart does not mean sep. We're at tLineStart because the fast branch above doesn't run when sep=' '
           fieldStart = tch;
           skip_white(&tch);
-          if (*tch=='\0') continue; // empty last line
+          if (*tch=='\0') {
+            nrowLimit = myNrow;
+            continue; // empty last line
+          }
           if (eol(&tch) && skipEmptyLines) { tch++; continue; }
           tch = fieldStart;         // in case tabs at the beginning of the first field need to be included
         }