Reset xtb_locales GN variable for each grd_files_info loop iteration.

If a generate_embedded_i18n target is specified with multiple
grd_files_info entries each of the entries can have different
xtb_locales configurations. However, unless the xtb_locales variable
is reset to [] before it's updated, then the GN generation will fail.

Change-Id: I40d89b5e4da66570c61e03971d534518e5a4873d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1932800
Commit-Queue: Yngve Pettersen <yngve@vivaldi.com>
Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#719315}

base/win/embedded_i18n/generate_embedded_i18n.gni

@@ -122,6 +122,8 @@ template("generate_embedded_i18n") {
         xtb_relative_path,
       ]
 
+      # Lists must be reset to empty before being assigned a new list
+      xtb_locales = []
       xtb_locales = grd_file_info[3]
 
       foreach(locale, xtb_locales) {