sysroot: Make devpath more clear

Coverity points out that we have a memory leak from g_strdup(devpath).
This is a mistake from coverity. However, we use `g_path_get_dirname()`
which makes the process clearer since it does not modify the string in
place.

src/libostree/ostree-sysroot.c

@@ -2240,10 +2240,19 @@ ostree_sysroot_deployment_unlock (OstreeSysroot *self, OstreeDeployment *deploym
         g_autofree char *devpath
             = unlocked_state == OSTREE_DEPLOYMENT_UNLOCKED_DEVELOPMENT
                   ? _ostree_sysroot_get_runstate_path (
-                        deployment, _OSTREE_SYSROOT_DEPLOYMENT_RUNSTATE_FLAG_DEVELOPMENT)
+                      deployment, _OSTREE_SYSROOT_DEPLOYMENT_RUNSTATE_FLAG_DEVELOPMENT)
                   : _ostree_sysroot_get_runstate_path (
-                        deployment, _OSTREE_SYSROOT_DEPLOYMENT_RUNSTATE_FLAG_TRANSIENT);
-        g_autofree char *devpath_parent = dirname (g_strdup (devpath));
+                      deployment, _OSTREE_SYSROOT_DEPLOYMENT_RUNSTATE_FLAG_TRANSIENT);
+
+        g_autofree char *devpath_parent = "";
+        if (devpath[strlen (devpath) - 1] == G_DIR_SEPARATOR)
+          {
+            g_autofree char *modifed_devpath = g_strdup (devpath);
+            modifed_devpath[strlen (modifed_devpath) - 1] = '\0';
+            devpath_parent = g_path_get_dirname (modifed_devpath);
+          }
+        else
+          devpath_parent = g_path_get_dirname (devpath);
 
         if (!glnx_shutil_mkdir_p_at (AT_FDCWD, devpath_parent, 0755, cancellable, error))
           return FALSE;