parse: correctly handle fread() errors

If no CCID reader is found then the size of the output.txt file is 0
bytes and fread(3) returns 0 but that is not an error.

src/parse.c

@@ -264,9 +264,9 @@ int main(int argc, char *argv[])
 		char buff[256];
 
 		s = fread(buff, 1, sizeof buff, fd);
-		if (0 == s)
+		if (0 == s && ferror(fd))
 		{
-			perror("fread");
+			perror("fread " OUTPUT_FILENAME);
 			return -1;
 		}
 		fwrite(buff, s, 1, stdout);