tree-wide: fix return value handling of base64mem()

This returns an ssize_t, not an int. On populare archs that's the
difference between 64bit and 32bit. hence, let's be more careful here,
and not silently drop half the bits on the ground by assigning the
return value to "int".

As noticed by @malikabhi05:

https://github.com/systemd/systemd/pull/24754#discussion_r1062903159

src/cryptsetup/cryptsetup-tokens/cryptsetup-token-systemd-tpm2.c

@@ -51,6 +51,7 @@ _public_ int cryptsetup_token_open_pin(
                 .search_pcr_mask = UINT32_MAX
         };
         uint16_t pcr_bank, primary_alg;
+        ssize_t base64_encoded_size;
         TPM2Flags flags = 0;
         const char *json;
         int r;
@@ -116,13 +117,13 @@ _public_ int cryptsetup_token_open_pin(
                 return log_debug_open_error(cd, r);
 
         /* Before using this key as passphrase we base64 encode it, for compat with homed */
-        r = base64mem(decrypted_key, decrypted_key_size, &base64_encoded);
-        if (r < 0)
-                return log_debug_open_error(cd, r);
+        base64_encoded_size = base64mem(decrypted_key, decrypted_key_size, &base64_encoded);
+        if (base64_encoded_size < 0)
+                return log_debug_open_error(cd, base64_encoded_size);
 
         /* free'd automatically by libcryptsetup */
-        *ret_password_len = strlen(base64_encoded);
         *ret_password = TAKE_PTR(base64_encoded);
+        *ret_password_len = base64_encoded_size;
 
         return 0;
 }