Do not try to rematch patterns with ^ or $

It is impossible to rematch a pattern which has one (or both)
of these operators, so the simplest solucion is detect them
while we are compiling the regular expression and break the
match loop after the first iteration.

ed.c

@@ -63,6 +63,7 @@ static char *rhs;
 static char *lastmatch;
 static struct undo udata;
 static int newcmd;
+int eol, bol;
 
 static void
 discard(void)
@@ -358,11 +359,15 @@ compile(int delim)
 	if (!isgraph(delim))
 		error("invalid pattern delimiter");
 
-	bracket = siz = 0;
+	eol = bol = bracket = siz = 0;
 	for (n = 0;; ++n) {
 		if ((c = input()) == delim && !bracket)
 			break;
-		if (c == '\n' || c == EOF) {
+		if (c == '^') {
+			bol = 1;
+		} else if (c == '$') {
+			eol = 1;
+		} else if (c == '\n' || c == EOF) {
 			back(c);
 			break;
 		}
@@ -1005,9 +1010,11 @@ subline(int num, int nth)
 	static size_t siz, cap;
 
 	i = changed = siz = 0;
-	for (m = match(num); m && *lastmatch != '\n'; m = rematch(num)) {
+	for (m = match(num); m; m = rematch(num)) {
 		addpre(&s, &cap, &siz);
 		changed |= addsub(&s, &cap, &siz, nth, ++i);
+		if (eol || bol)
+			break;
 	}
 	if (!changed)
 		return;