fixed uninitialized variable (cppcheck)

core/io/file_access_memory.cpp

@@ -132,7 +132,7 @@ bool FileAccessMemory::eof_reached() const {
 
 uint8_t FileAccessMemory::get_8() const {
 
-	uint8_t ret;
+	uint8_t ret = 0;
 	if (pos < length) {
 		ret = data[pos];
 	};