ext/sodium: Avoid shifts wider than 32 bits on size_t values

Backport from PECL libsodium-php 2.0.10

Author: jedisct1

ext/sodium/libsodium.c

@@ -3405,7 +3405,8 @@ PHP_FUNCTION(sodium_pad)
 	for (j = 0U; j <= xpadded_len; j++) {
 		ZSTR_VAL(padded)[j] = unpadded[i];
 		k -= st;
-		st = (~(((((k >> 48) | (k >> 32) | (k >> 16) | k) & 0xffff) - 1U) >> 16)) & 1U;
+		st = (size_t) (~(((( (((uint64_t) k) >> 48) | (((uint64_t) k) >> 32) |
+							 (k >> 16) | k) & 0xffff) - 1U) >> 16)) & 1U;
 		i += st;
 	}
 #if SODIUM_LIBRARY_VERSION_MAJOR > 9 || (SODIUM_LIBRARY_VERSION_MAJOR == 9 && SODIUM_LIBRARY_VERSION_MINOR >= 6)