Fix incorrect bitshifting in ffi

When a uint8_t is bitshifted to the left, it is actually promoted to an
int. For the current code this has the effect of a wrong sign-extension,
and the result will also wrongly become zero when insert_pos >= 32.
Fix this by adding an explicit cast.

Author: nielsdos

ext/ffi/ffi.c

@@ -599,15 +599,15 @@ static uint64_t zend_ffi_bit_field_read(void *ptr, zend_ffi_field *field) /* {{{
 
 	/* Read full bytes */
 	while (p < last_p) {
-		val |= *p++ << insert_pos;
+		val |= (uint64_t) *p++ << insert_pos;
 		insert_pos += 8;
 	}
 
 	/* Read partial suffix byte */
 	if (p == last_p) {
 		size_t num_bits = last_bit % 8 + 1;
 		mask = (1U << num_bits) - 1U;
-		val |= (*p & mask) << insert_pos;
+		val |= (uint64_t) (*p & mask) << insert_pos;
 	}
 
 	return val;