Include string.h to sugar-fatattr

According to dsd's wisdom, without being
included, strerror is undeclared.

Fixes #4600 sugar crashing when copying
journal entries to documents folder.

Signed-off-by: Martin Abente Lahaye <tch@sugarlabs.org>

src/sugar3/sugar-fatattr.c

@@ -30,6 +30,7 @@
 
 #include <errno.h>
 #include <stdio.h>
+#include <string.h>
 
 // This function is wrapped by getattrs/setattrs
 static int _ioctl_attrs(char *file, __u32 *attrs, int ioctlnum, char *verb)