build/make/version.sh: Fix read of git hash when there are no tags.

'git describe ...' cannot be used when a repo has no tags. Use
'git rev-parse ...' instead when 'git tag' produces no output.

BUG=https://bugs.chromium.org/p/aomedia/issues/detail?id=4

Change-Id: Idb0c0c739390b4d919475d2b6c91542ada4f7bb2

build/make/version.sh

@@ -25,7 +25,12 @@ git_version_id=""
 if [ -d "${source_path}/.git" ]; then
     # Source Path is a git working copy. Check for local modifications.
     export GIT_DIR="${source_path}/.git"
-    git_version_id=`git describe --match=v[0-9]* 2>/dev/null`
+    git_tags=`git tag -l 'v[0-9]*'`
+    if [ -n "${git_tags}" ]; then
+      git_version_id=`git describe --match=v[0-9]* 2>/dev/null`
+    else
+      git_version_id=`git rev-parse --short HEAD`
+    fi
 fi
 
 changelog_version=""