change PIIODevice read* and write* methods size to "ssize_t"

libs/main/io_devices/pifile.cpp

@@ -447,13 +447,13 @@ PIByteArray PIFile::get() {
 }
 
 
-int PIFile::readDevice(void * read_to, int max_size) {
+ssize_t PIFile::readDevice(void * read_to, ssize_t max_size) {
 	if (!canRead() || PRIVATE->fd == 0) return -1;
 	return fread(read_to, 1, max_size, PRIVATE->fd);
 }
 
 
-int PIFile::writeDevice(const void * data, int max_size) {
+ssize_t PIFile::writeDevice(const void * data, ssize_t max_size) {
 	if (!canWrite() || PRIVATE->fd == 0) return -1;
 	return fwrite(data, 1, max_size, PRIVATE->fd);
 }