stripspace: incomplete line fix (take #2)

This fixes f4ee3eb689 breakage, which
added an extra trailing blank line after stripping trailing blank lines
by mistake.

Signed-off-by: Junio C Hamano <junkio@cox.net>

stripspace.c

@@ -12,7 +12,9 @@ static int cleanup(char *line)
 {
 	int len = strlen(line);
 
-	if (len > 1 && line[len-1] == '\n') {
+	if (len && line[len-1] == '\n') {
+		if (len == 1)
+			return 0;
 		do {
 			unsigned char c = line[len-2];
 			if (!isspace(c))