test_must_be_empty: simplify file existence check

Commit 11395a3 (test_must_be_empty: make sure the file exists, not
just empty, 2018-02-27) basically duplicated the 'test_path_is_file'
helper function in 'test_must_be_empty'.

Just call 'test_path_is_file' to avoid this code duplication.

Signed-off-by: SZEDER Gábor <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: szeder

t/test-lib-functions.sh

@@ -718,11 +718,8 @@ verbose () {
 # otherwise.
 
 test_must_be_empty () {
-	if ! test -f "$1"
-	then
-		echo "'$1' is missing"
-		return 1
-	elif test -s "$1"
+	test_path_is_file "$1" &&
+	if test -s "$1"
 	then
 		echo "'$1' is not empty, it contains:"
 		cat "$1"