avoid whitespace on empty line in automatic usage message

When outputting a usage message with a blank line in the
header, we would output a line with four spaces. Make this
truly a blank line.

This helps us remove trailing whitespace from a test vector.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

parse-options.c

@@ -312,8 +312,12 @@ void usage_with_options_internal(const char * const *usagestr,
 	fprintf(stderr, "usage: %s\n", *usagestr++);
 	while (*usagestr && **usagestr)
 		fprintf(stderr, "   or: %s\n", *usagestr++);
-	while (*usagestr)
-		fprintf(stderr, "    %s\n", *usagestr++);
+	while (*usagestr) {
+		fprintf(stderr, "%s%s\n",
+				**usagestr ? "    " : "",
+				*usagestr);
+		usagestr++;
+	}
 
 	if (opts->type != OPTION_GROUP)
 		fputc('\n', stderr);

t/t1502-rev-parse-parseopt.sh

@@ -5,7 +5,7 @@ test_description='test git rev-parse --parseopt'
 
 cat > expect.err <<EOF
 usage: some-command [options] <args>...
-    
+
     some-command does foo and bar!
 
     -h, --help            show the help