seq: fix selecting subthreads at the end of sequences and add test cases

seq.c

@@ -266,8 +266,10 @@ parse_subthread(char *map, long a, long *stopo)
 
 	for (s = map, line = 0; s; s = t+1) {
 		t = strchr(s, '\n');
-		if (!t)
+		if (!t) {
+			minindent = -1;
 			break;
+		}
 		line++;
 		int indent = 0;
 		while (*s && iswsp(*s)) {

t/7000-mseq.t

@@ -1,7 +1,7 @@
 #!/bin/sh -e
 cd ${0%/*}
 . ./lib.sh
-plan 8
+plan 10
 
 rm -rf test.dir
 mkdir test.dir
@@ -32,4 +32,13 @@ check_test  'subthread' -eq 2 'mseq 7_ | wc -l'
 check 'parent' 'mseq 6^ | grep "inbox/cur/5_1:2,"'
 check_test 'range' -eq 3 'mseq 1:3 | wc -l'
 
+cat <<! >seq
+inbox/cur/1:2,
+ inbox/cur/2:2,
+  inbox/cur/3:2,
+!
+
+check_test  'whole thread at the end' -eq 3 'mseq 2= | wc -l'
+check_test  'subthread at the end' -eq 2 'mseq 2_ | wc -l'
+
 )