pw_stream: Don't memmove with zero bytes

Bug: 527
Change-Id: Iab4f1789ca64273a8c20c5f9fba1b90050b1a3ac
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/68586
Reviewed-by: Ewout van Bekkum <ewout@google.com>
Commit-Queue: Ted Pudlik <tpudlik@google.com>
diff --git a/pw_stream/memory_stream.cc b/pw_stream/memory_stream.cc
index 173a9e3..37894b1 100644
--- a/pw_stream/memory_stream.cc
+++ b/pw_stream/memory_stream.cc
@@ -30,6 +30,9 @@
   }
 
   size_t bytes_to_write = data.size_bytes();
+  if (bytes_to_write == 0) {
+    return OkStatus();
+  }
   std::memmove(dest_.data() + position_, data.data(), bytes_to_write);
   position_ += bytes_to_write;