Fix Coverity defect #1457195

Author: 3XX0

src/utils.c

@@ -429,7 +429,7 @@ make_ancestors(char *path, mode_t perm)
 }
 
 int
-file_create(struct error *err, const char *path, void *data, uid_t uid, gid_t gid, mode_t mode)
+file_create(struct error *err, const char *path, const char *data, uid_t uid, gid_t gid, mode_t mode)
 {
         char *p;
         uid_t euid;
@@ -461,6 +461,10 @@ file_create(struct error *err, const char *path, void *data, uid_t uid, gid_t gi
                 if (mkdir(path, perm) < 0 && errno != EEXIST)
                         goto fail;
         } else if (S_ISLNK(mode)) {
+                if (data == NULL) {
+                        errno = EINVAL;
+                        goto fail;
+                }
                 if (symlink(data, path) < 0 && errno != EEXIST)
                         goto fail;
         } else {

src/utils.h

@@ -61,7 +61,7 @@ const char **array_append(const char **, const char * const [], size_t);
 
 void *file_map(struct error *, const char *, size_t *);
 int  file_unmap(struct error *, const char *, void *, size_t);
-int  file_create(struct error *, const char *, void *, uid_t, gid_t, mode_t);
+int  file_create(struct error *, const char *, const char *, uid_t, gid_t, mode_t);
 int  file_remove(struct error *, const char *);
 int  file_exists(struct error *, const char *);
 int  file_mode(struct error *, const char *, mode_t *);