[zbitl] Fix minor error string bug

A space was missing.

Change-Id: I5a54ca4cd49079c0fde179e1a8cd41afbde52d22
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/445934
Fuchsia-Auto-Submit: Joshua Seaton <joshuaseaton@google.com>
Reviewed-by: Roland McGrath <mcgrathr@google.com>
Testability-Review: Roland McGrath <mcgrathr@google.com>
Commit-Queue: Joshua Seaton <joshuaseaton@google.com>

zircon/system/ulib/zbitl/include/lib/zbitl/error_string.h

diff --git a/zircon/system/ulib/zbitl/include/lib/zbitl/error_string.h b/zircon/system/ulib/zbitl/include/lib/zbitl/error_string.h
index 9da810e..075e1538 100644
--- a/zircon/system/ulib/zbitl/include/lib/zbitl/error_string.h
+++ b/zircon/system/ulib/zbitl/include/lib/zbitl/error_string.h
@@ -16,7 +16,7 @@
 template <typename ViewError>
 std::string ViewErrorString(const ViewError& error) {
   std::string s{error.zbi_error};
-  s += "at offset ";
+  s += " at offset ";
   s += std::to_string(error.item_offset);
   if (error.storage_error) {
     s += ": ";