ed: Don't clear modflag in shell escapes

The function dowrite() is used for normal writes and for shell
escapes and in the second case we don't have the actual file
saved to disk.

ed.c

@@ -795,7 +795,8 @@ dowrite(const char *fname, int trunc)
 	if (r)
 		error("input/output error");
 	strcpy(savfname, fname);
-	modflag = 0;
+	if (!sh)
+		modflag = 0;
 	curln = line;
 	if (optdiag)
 		printf("%zu\n", bytecount);

tests/0017-ed.sh

@@ -0,0 +1,11 @@
+#!/bin/sh
+
+../ed -s /dev/null <<EOF | grep 'file modified' > /dev/null
+a
+1
+2
+.
+w !echo
+q
+h
+EOF