Don't fail if there are no comments.

Grep exits with non-zero if it find no matches. But it doesn't matter in
this case, so just carry on.

Test: frameworks/base/tools/hiddenapi/sort_api.sh \
Test:    frameworks/base/config/hiddenapi-light-greylist.txt
Change-Id: I7c219ee617f7dfa3cff5232ab979cc4ba38ebbfd
diff --git a/tools/hiddenapi/sort_api.sh b/tools/hiddenapi/sort_api.sh
index bdcc807..76a2f2d 100755
--- a/tools/hiddenapi/sort_api.sh
+++ b/tools/hiddenapi/sort_api.sh
@@ -12,8 +12,8 @@
 # Sort
 IFS=$'\n'
 # Stash away comments
-C=( $(grep -E '^#' <<< "${A[*]}") )
-A=( $(grep -v -E '^#' <<< "${A[*]}") )
+C=( $(grep -E '^#' <<< "${A[*]}" || :) )
+A=( $(grep -v -E '^#' <<< "${A[*]}" || :) )
 # Sort entries
 A=( $(LC_COLLATE=C sort -f <<< "${A[*]}") )
 A=( $(uniq <<< "${A[*]}") )