dd: Consider block count in inner read loop

When ibs is smaller than obs, checking the block count in the outer
loop is not sufficient; we need to break out of the inner read loop
once we've read the specified number of blocks.

Thanks to phoebos for reporting this issue.

dd.c

@@ -173,8 +173,12 @@ main(int argc, char *argv[])
 			eprintf("lseek:");
 		/* XXX: handle non-seekable files */
 	}
-	while (!eof && (count == -1 || ifull + ipart < count)) {
+	while (!eof) {
 		while (ipos - opos < obs) {
+			if (ifull + ipart == count) {
+				eof = 1;
+				break;
+			}
 			ret = read(ifd, buf + ipos, ibs);
 			if (ret == 0) {
 				eof = 1;