Fix off-by-one affecting benchmark numbers in folly/io.

Summary: Fix off-by-one affecting benchmark numbers in folly/io.

Test Plan:
$ fbconfig -r folly/io/test
$ fbmake --fast opt
$ _build/opt/folly/io/test/iobuf_cursor_test --benchmark
$ _build/opt/folly/io/test/iobuf_network_bench --benchmark

Reviewed By: simpkins@fb.com

FB internal diff: D1199679

Blame Revision: D344018

folly/io/test/IOBufCursorTest.cpp

@@ -591,20 +591,20 @@ void runBenchmark() {
 }
 
 BENCHMARK(rwPrivateCursorBenchmark, iters) {
-  while (--iters) {
+  while (iters--) {
     runBenchmark<RWPrivateCursor>();
   }
 }
 
 BENCHMARK(rwUnshareCursorBenchmark, iters) {
-  while (--iters) {
+  while (iters--) {
     runBenchmark<RWUnshareCursor>();
   }
 }
 
 
 BENCHMARK(cursorBenchmark, iters) {
-  while (--iters) {
+  while (iters--) {
     Cursor c(iobuf_read_benchmark.get());
     for(int i = 0; i < benchmark_size ; i++) {
       c.read<uint8_t>();
@@ -614,7 +614,7 @@ BENCHMARK(cursorBenchmark, iters) {
 
 BENCHMARK(skipBenchmark, iters) {
   uint8_t buf;
-  while (--iters) {
+  while (iters--) {
     Cursor c(iobuf_read_benchmark.get());
     for(int i = 0; i < benchmark_size ; i++) {
       c.peek();

folly/io/test/NetworkBenchmark.cpp

@@ -31,7 +31,7 @@ size_t buf_size = 0;
 size_t num_bufs = 0;
 
 BENCHMARK(reserveBenchmark, iters) {
-  while (--iters) {
+  while (iters--) {
     unique_ptr<IOBuf> iobuf1(IOBuf::create(buf_size));
     iobuf1->append(buf_size);
     for (size_t bufs = num_bufs; bufs > 1; bufs --) {
@@ -42,7 +42,7 @@ BENCHMARK(reserveBenchmark, iters) {
 }
 
 BENCHMARK(chainBenchmark, iters) {
-  while (--iters) {
+  while (iters--) {
     unique_ptr<IOBuf> iobuf1(IOBuf::create(buf_size));
     iobuf1->append(buf_size);
     for (size_t bufs = num_bufs; bufs > 1; bufs --) {
@@ -75,7 +75,7 @@ inline void poolPutIOBuf(unique_ptr<IOBuf>&& buf) {
 }
 
 BENCHMARK(poolBenchmark, iters) {
-  while (--iters) {
+  while (iters--) {
     unique_ptr<IOBuf> head = std::move(poolGetIOBuf());
     for (size_t bufs = num_bufs; bufs > 1; bufs --) {
       unique_ptr<IOBuf> iobufNext = std::move(poolGetIOBuf());