Avoid clang warnings from implicit off_t->size_t cast

src/common/crypto_curve25519.c

@@ -169,7 +169,7 @@ curve25519_keypair_read_from_file(curve25519_keypair_t *keypair_out,
 
  end:
   if (content) {
-    memwipe(content, 0, st.st_size);
+    memwipe(content, 0, (size_t) st.st_size);
     tor_free(content);
   }
   if (r != 0) {

src/test/test_crypto.c

@@ -1097,7 +1097,7 @@ test_crypto_curve25519_persist(void *arg)
   tor_free(tag);
 
   content[69] ^= 0xff;
-  tt_int_op(0, ==, write_bytes_to_file(fname, content, st.st_size, 1));
+  tt_int_op(0, ==, write_bytes_to_file(fname, content, (size_t)st.st_size, 1));
   tt_int_op(-1, ==, curve25519_keypair_read_from_file(&keypair2, &tag, fname));
 
  done: