Fix minui cleanup path on error.

  bootable/recovery/minui/resources.cpp:321:21: warning: Branch condition evaluates to a garbage value
                if (surface[i]) free(surface[i]);
                    ^~~~~~~~~~
  bootable/recovery/minui/resources.cpp:424:13: warning: Value stored to 'len' during its initialization is never read
        int len = row[4];
            ^~~   ~~~~~~

Bug: http://b/27264652
Change-Id: Icc1a914c59d6a89dab1b752b2cd2b40549566481