path-util: don't add extra "/" when prefix already is suffixed by slash

No need to insert duplicate "/" if we can avoid it. This is particularly
relevant if the prefix passed in is the root directory.

src/basic/path-util.c

@@ -84,6 +84,9 @@ char *path_make_absolute(const char *p, const char *prefix) {
         if (path_is_absolute(p) || isempty(prefix))
                 return strdup(p);
 
+        if (endswith(prefix, "/"))
+                return strjoin(prefix, p);
+        else
                 return strjoin(prefix, "/", p);
 }